Ow come on, you post (nearly) every 10 minutes!
It's a question of what you want to achieve. High frequencies- take the 4000er, low latencies- take the xl.
Hmm, i don't know if in the USA A-DATA is well-known ( or even known?), but the PC4000 A-DATA seem to be nearly perfect for Athlon 64.
Even better than OCZ's EB, doing even higher- at last 270 with just 2,8v
I'm not a friend of high voltages, so I'm pretty sympathic with them
Um, it depends what you are using. For AMD XPs, the NF7-S will go up to 250 FSB or DDR500. For P4s, the Asus P4C800-E Deluxe will OC that high and beyond. No motherboard is rated as running DDR500 but many will overclock that high. What processor are you using or will you be using?