Depending on the fan, Your 6035 will handle the xp1700, but probably not for overclocking. The 6035 has been kinda forgotten in the rush to newer stuff, but will hang right in there with many of the more recent models.
You're right, the 8045 is a monster, I have a homeless one sitting on my desk. An overclocker's dream, even with a relatively quiet ~40cfm fan. From what I've seen, the point of diminished returns for fanpower is very low, just because the 8045 is so effective. Just be sure to buy a compatible mobo, these things are really really big....