When buying cards for SLI, do the cards have to be the exact same? In other words, I have an MSI 6800 128mb. Does that mean I have to buy another MSI, or can I buy an XFX?

"White men can jump"

sell the 6800 & buy a single 7800GTX

Hellz Yea!

^^^
Definitely a better idea.

jajaja
no one ever answers the questions
xD
I don't know if you need the exact same brand.
However I also support the idea of a 7800gt. GTX not worth it.

Free

It's best to buy the same brand and model. You risk it not working otherwise. Sometimes it will work, but you never know unless you get the exact same card.

Corn chips are no place for a mighty warrior!

It has been my understanding that the GPU's must be identical. I can't find any definitive answer on nVidia's site, but here is a quote from Tom's Hardware (link) when SLI was first being launched, so the requirements could have changed:

"For Multi-GPU to work, both cards need to be of the same performance class, meaning you can only pair either two GeForce 6800 Ultras, two GeForce 6800 GTs or two GeForce 6800s (standard). Mixing these cards will not work, although it should in theory, due to the dynamic load-balancing capability."

However, I would also not mix cards of the same GPU if one has been overclocked. Basically it looks to be the same as dual channel memory. The specs of the pieces must be the same - they don't have to come fromt he same manufacturer, but you rule out at least one factor should you run into problems.

Michael J