4GB of memory is more than sufficient, so 2xDIMM slots is a non issue, so is the higher USB port count, unless you have appropriate peripherals to use them all at the same time.
The best option, like previously said is the Gigabyte G31 ES2L. Its overclocking potential nearly matches up to most P35 boards. I'm guessing your processor is a E7400, you could easily do ~3.4 Ghz with this board. Invest the remaining money on an OCZ Vendetta 2 or the likes.