The downgraded buss speed on the AM2+ boards is not noticable.
A question I have for you, why are picking boards with an nVidia chipset on them?
The boards you have picked do not support SLI, so there is absolutely no reason to buy one with an inferior nVidia chipset. If you are only running 1 video card, you want a board with an AMD chipset on it, even if your GPU is nVidia.
I am running a Phenom II 920 on a MA78GM-US2H, and a 8800GTS 512 OC video card. It scores just over 15,000 in 3D Mark 06. That is not too shabby for an $80 motherboard and old 8800 video card.