A 5830 will never saturate the x8 lane anyway. You will see no performance difference what so ever at x8 and x16 with that card. Nothing changes with them matching or not.
Do you have your cards in the right slots for x16 x16? To get them both at x16 you must have the first card in the top slot, and the second card in the LAST slot. If you have the second card in the second slot and not third, then that card will run x8, as shown by page 2-29 of your manual.
>.< Now I feel silly. I could swear I read that thing about 50 times, too. If that's what it's going to take, then i'll probably have to forego the option. I tried that when i was initially setting up the rig, but something to do with my case not having enough room prohibited it. Also, I don't think my MoBo came with a crossfire bridge long enough to reach the bottom slot. I may revisit the idea, however, so thank you very much for catching that.