it depends if you are a heavy gamers that demands that everything is maxed out or you wont play the game
the gain is not so little it ranges from 50-70% depending on the componants and the configuration you are using
again you wont notice the difference unless you have high resolution monitor or hd tv
so it is worth a sli configuration for 20'' and higher monitors or high def tv
but if you have a 19'' monitor (or less) even with a sli configuration you wont benefit from it even if you max out everything
sli=Scalable Link Interface
interleaving is one of four way that nvidia uses sli to process the image
ati crossfire uses same principals but in a different way
A 7800GTX 512Mb at very high res 2048x1536 with 4xAA performs identically to a 256Mb version. So adding the extra memory will not boost gaming performance as it is "today" but for future games the difference will show. It all comes down to the core and memory clock. Comparing the 7800GTX which runs at a core clock of 550Mhz and 7800GT which runs at 430Mhz we can see that the 7800GTX clearly outperforms(over 40%) the 7800GT in any game and at very high resolutions.

Also we do realise that most games today barely support SLI so we will see a SLI Boost in upcoming games.
Thank U for the answers Karim and Darkstar, I am getting really old Karim Forgive me I should have checked on the "SLI" acrom before I typed so fast.
Darkstar: you hit the nail on the head, my whole discussion here was to get to this statment :
""It all comes down to the core and memory clock"" That is why I ask about the bus Limitation or bottleneck in the first Email. But you are 100% correct.
Things will change you will see a lot faster clocks soon, and by the way clocks are a nightmare in my Job, if you do not have a clock nothing will fire up, neither the chipset otr the mother boards " you will never come out of Reset mode " better have a good clock generating moduler and a good clock tree, and watch out when your clock cross different frequency domains. anyway, Thank you Karim and Darkstar, it is a pleasure to continue discussions with you.
Chips
Darkstar, Please correct me if I am wrong, The more Memory you have the better and faster graphic you will have, as you know the video card will use the VRAM on it as a buffer where he will keep the most used file in this buffer, so it is really acting as a cache for the video card, so the bigger the amount of the cache makes a bigger buffer, and that will save the video card from running all the way to the system memory to get the files that he needs to process. as you know games that do a lot of texturing and details requires a lot bigger VRAM cache on the card.
Sabaho Karim, I see you R on line so I thought I drop a hello to you too and I appreciate your feedback on this issue too.
Chips
Video RAM (VRAM) is a buffer between the computer processor and the display and is often called the frame buffer.VRAM is dual ported which means that the cpu can write to the vram and the gpu can read from it at the same time with no delay(Which greatly differs from how RAM works). When images are to be sent to the display, they are first read by the processor as data from RAM and then written to video RAM. From video RAM (the frame buffer), the data is converted by a RAM digital-to-analog converter (RAMDAC) into analog signals that are sent to the display presentation mechanism such as a cathode ray tube (CRT).Some cards have multiple RAMDACs, which can improve performance and support more than one monitor.


VRAM is expensive (VRAM is more complex and requires more silicon per bit than standard DRAM, which makes it cost more)so u cannot find huge quantities of it but instead now manifacurers use SGRAM (synchronous graphics RAM) instead.Its performance is nearly the same, but SGRAM is cheaper. Concerning performance well yes the more vram it holds the more completed images it can carry at a time to display them. Too much VRAM (which is unlikely) can definetly cause a bottleneck at the GPU.To avoid confusion, VRAM makes up only a 'portion' of the RAM (ie:ram present on the vga), the rest of the memory is used to store the neccessary pixels and images.

Hope this helps and you are most welcomed.
in my opinion nVidia and ATI should creat craphic card same as todays mainboards u can upgrade the processor and the memry on it, but this will only be acheived in the futur, but as for now i have worked on the MSI 7800GTX 256 GDDR3 and well, in
SLI mode if ur not using your computer for rendering and graphical aplications beter than games then u dont need it, overpriced @ 680usd (vat not included) its a waste of money,a 6800gt will be more than enaugh
, plus one problem is known and thats the cooling system is not enaug! running @ 450mhz the msi 7800 gtx cant be overclocked unless in a freezer!!!!!! ....... the next step to get the more out of your hardware is too get rid of the slow softwares,and by installing the windows xp 64bit edition ull be doing this, upgrade ur rams to 8gb and this will be a hell of a pc , i tryed it ;) : pentium D3.2ghz 2x1mb MSI 7800gtx 256 Gddr3 MSi P4N-sli 4gb Kingstone
the only limitation was the operating system .
6 days later
Hi Ulais, I am just curious, You mentioned that you worked on the video card with GDDR3, what brand name are these GDDR3 Dimms that were used ? what did you do on that card ? Any idea about the transfer rate and what kind speed that bus have?
Chips
theses are not dimms but the type of rams on the graphic card
the speeds vary from card to card
but mainly memory clock is around 1200 MHz (for a 7800gtx 256MB)
and an interface of 256 bit ramdac is 400MHz
Thank you Karim , I called them Dimms, they are a group of Chips that populate that card, If all these chips are the same speed "let us say 7 nano seconds speed" and the bus interface is the same and main memory clock is the same on all cards from that manufacturere, why would be a difference between cards as you stated? Is there a design difference any where between the cards . if not please elborate on why the speeds on the cards are different?
Thank U
Chips IMR
Some have better cooling leading to a better overclocking
These days the overclocking is done on the manufacturer level rather than the user's which in it turn will reduce the number of voided guaranty leading to less trouble for the manufacturer
As for the design I don't think there is much difference between the cards as the core is provided by nvidia and the ram mainly by samsung
So it all comes to how much power you can squeeze out of the card resulting in different core and memory clock speeds