I have been using and working with a few people who have written an Nvidia patch that will allow you to SLI "Mis-matched"  cards which Nvidia software does not allow.....  They want you to buy a matching card to boost phsyics and fps, as long as the DEV #'s match or if you can't run SLI on a X-fire only board.? I have been running it on a few machines for sometime with a gained fps and windows score. some of the top 3-d mark scores in the world for quad-SLI have been reached with this patch.   If you have a free pci-e slot an and old card that won't SLI with your new card, this patch might boost your fps if they have the same architecture. basically it might boost your rig with some of your old scrap pile parts. 'Which Nvidia does not like"      If you have an old card you want to match up with a new one to boost fps, send me a message on here or in steam and i will see if the cards have compatible architectures to run  an SLI patch and walk you thru it if you'd like.  Seanstizz7..

I run Nvidia, but last I checked Radeon cards mostly do this by default. As long as the cards are from the same series they are compatible for Crossfire.  I ran a 6850 and a 6870 like this for quite a while.

What about mismatched architectures?  What Helen's to the speed of the faster card? Having Crossfire,  I've  no need for this.   I'm just curious.

What does nvidia have to say about this? I would think that if it worked well enough to their liking,  they'd implement it themselves,  to better compete with ATI/AMD.  Is it a re-work of official drivers,  or an augmentation ?

Nvidia writes limitations into there software so that if the DEV #'s do not match perfectly the cards will not SLI. with this patch if the first 3 #s match you can SLI and set the lesser card for physics and gain fps.   http://www.techpowerup.com/forums/threads/sli-with-different-cards.158907/

NVIDIA actually does more then just right code to stop mismatching cards from working.  Nvidia actually test every card that is eligible for SLI on every configuration known.  And when I mean everything, I dont joke.  Every motherboard, memory, CPU configuration you can think of.  And if you are a hardware manufacture and you want SLI to work on your hardware, you have to send NVIDIA all your parts and Nvidia doesnt pay for it.  You should see their storage rooms, they are packed with a computer geeks wet dream.

There are softwares out there that are supposed to help override that part of the driver, but if you do find one that works, that doesnt mean you will get the full performance of SLI.