Credo che non sia più possibile
ho trovato un post del 2007 in cui si riportava una faq di slizone
(dove si dicevano le stesse cose che ha postato devilmaycry)
Overclock.net - Overclocking.net - View Single Post - can you sli two different cards ?
"Can I mix and match graphics cards with different sizes of memory?
While it is not recommended, NVIDIA does offer this flexibility using Coolbits. When purchasing a second graphics card, you should try to match the memory size so that you are ensured full value and performance from your purchase. For example, if your first card is a GeForce 6600 GT with 128MB of memory, you should purchase a second GeForce 6600 GT with 128MB of memory. However, using Coolbits (value set to 18), you can force both of the cards to use the lower of the two memory sizes and operate together in SLI mode. When dissimilar memory sizes are enabled to work together using Coolbits, the effective memory size for each card becomes the smaller of the two memory sizes. Instructions to enable this feature can be found here. How to Enable Coolbits"
andando però a leggere la sopracitata faq è stata modificata in
"Can I mix and match graphics cards with different sizes of memory?
No. For example, an XXXGT 512MB cannot be paired with a XXXGT 1GB in an SLI configuration."
Non so se questo sia valido per le 9800gt, credo che la cosa parta dalla serie 2xx
un tentativo si potrebbe fare