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Do you have a decent psu along with a motherboard that supports Sli and decent spacing?
It doesn't matter that much TBH. There is some effect from having the same clockspeeds but it's small; don't expect any benefit from having the same brand. That having been said, are you really okay with putting two visually distinct cards in your case... maybe I'm OCD but that would drive me mad lol.
you should buy the same, having two different gpu's would do my head in looking at them
you should buy the same, having two different gpu's would do my head in looking at them