idk which is faster, but each will be recieving a certain bandwidth af info from the motherboard, or a certain amount can pass through the socket, but with the 3rd it runs out and has to limit them, so the first 2 can get full and the last little info, or 1 gets full and the other 2 get half the info, but idk which will be fastest, and i doubt you'll ever need a 3rd 5870 unless going for 3 or more monitors all maxing resand settings, and i think you 920 may bottle them at that point, but fps may be so ho you won't be able to see.