Wow! This is some nice memory. It will fit EVERY usage scenario I can think of. You want to run tightest timings? Check. You want solid overclocking? Check. You need absolutely blazing clocks with a bit more relaxed timings? Check.
The Mushkin XP2-6400 are a great performer. They come with tight default timings of 4-4-3-10, most other manufacturers give you something with 5-5-x-x. Using extreme voltage is not required. It will perform fine at 1.8V. If you are looking to get more overclocking out of the memory, no problem. The voltage can be safely increased to 2.1V for an extra overclock.
So many good things have their price of course. Around $180 for 1 GB is definitely nothing for budget users, you can get 2 GB of no-name memory for that. But if you are an enthusiast looking for a future-proof memory with Conroe and AM2 around the corner this might be a good choice. In addition you get excellent tech support from Mushkin. Their tech support reps are most probably already visiting your favorite forum.