You can probably just overclock the FSB on your current board and get the same result. The E5800 is the best choice on all of these boards because of the high multiplier. The only reason not to use the E5800 is if your board could support the E8000 series wolfdale processors, and I don't know of any AGP equipped boards that are capable of a 1333mhz FSB.
Maybe you could get a E8000 series with an unlocked multiplier to run at a lower FSB and then just up the multi. I don't know if anyone has tried it, but if you could it would be marginally faster. The only difference is the L2 cache size; it is 6mb on the wolfdale processors and 2mb on the E5000 series, but that doesn't make as much of a difference as you might think.