Neither, Sapphire's 780G is the only 780G board with 5 phase power, which is important for decent overcloocking.
If you're overclocking a Phenom though, you'll want a board with the new SB750 southbridge.
And there is no one motherboard is better than another. There is no rule stating "ASUS is good for overclocking".
9800GTS doesn't exist, perhaps you're talking about the 9800GTX or 8800GTS? The HD 4850 is in the same price range but is faster than both.
GTX GTX