I have 2 ATI Radeon cards in SLI mode. But it seems games run better when i run them on single card.... why?

I have 2 Radeon 5800 cards. When I run deus ex on a single card it runs smooth no probs. But when I run it on SLI crossfire mode, it seems slightly choppy in frame rate... Pls help why this is happening. I have payed lot of money for my second video card. I hope I didn't waste that money..I have 2 ATI Radeon cards in SLI mode. But it seems games run better when i run them on single card.... why?
Judging from "SLI" mode I am going to guess you don't know much about this. I would say you need to update drivers, MAKE SURE YOUR MOTHERBOARD SUPPORTS IT. Go into CCC (Catalyst control center) and make sure you have the option for crossfire checked.I have 2 ATI Radeon cards in SLI mode. But it seems games run better when i run them on single card.... why?
There may be a single driver version that might work with that particular model. Could be a year old. outdated driver that works better so these types of errors won't happen. That is why you will have driver profiles that can be to to autorun because some drivers are game specific. Radeon knows their own product. Call customer service line. They should be under warranty and the know a lot more than I would.I have 2 ATI Radeon cards in SLI mode. But it seems games run better when i run them on single card.... why?
First off, you're running them in Crossfire. SLI is for Nvidia cards. You're seeing lovely microstutters. Make sure you have the latest video drivers, the latest BIOS for your board, and the latest firmware for the cards. What board and CPU do you have?