you cant change the Bus, but only the multiplie, so no need to over clock or underclock the components.
even if you insert PC3200, you wont find significant performance Boost, so better is to be with it. or else you'll end up saying (what the Hell!!)
CPU has actually 2 speeds, one is called internal and other External, internal refers to that CLock that is 3200+ and external is 400 (the 200Mz DDR), it will never effect ur CPU's performance in anyway. not to worry, Be Happy!!
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"