I'd recommend bumping up to the Athlon XP 2500+ with a 333MHz core--the Barton. It's also perfectly matched to PC2700 RAM, which also runs at 333, as does the motherboard. I would also recommend a
Zalman flower heatsink. They cool very well and run almost silently.
As for RAM, brand reliability rates high on the list, and you'll end up paying for that reliability. Cheaper RAM also tends to have higher timings, sometimes making it actually slower than RAM that rated at a lower clock speed. Corsair, Mushkin, Micron are your friends. OCZ and PNY are...not. High clock speeds, but higher timings as well. Lower quality RAM, so they have to raise the timings in order to sell it at a certain rated speed. It's like upgrading to a 6-cylinder engine that's only giving you 20 more horsepower over a 4-cylinder.