DDR2 Dominator Question(s)

I am getting ready to finish my latest AMD driven build. This one will start with the latest AMD 3.4GHz AM3 processor, and will be overclocked, mildly at first. I am going to install the CPU on an Asus M478A PRO mother board. Normally I use 2 (2x2GB) Corsair XMS2 DDR2 800 RAM modules (the 5-5-5-18 rated modules) for a total of 8GB. I haven't until now gotten into OCing RAM, but am ready for that step at this point. My question is about what would be better for the 8GBs of RAM I'm going to use and try, at least, to overclock. Should I save some money and stick with 2 of the 4 GB sets of the XMS2 DDR2 800 or should I move up to the XMS2 DHX DDR2 800 sticks with the CAS 4 rating? Is there an advantage to this memory over the regular XMS2 without the DHX technology? The other thing I am wondering is if there is a reason why on Newegg the sets of 4 of the 2GB sticks (the 8 GB package) seems to have less negative posts than the sets of 2 (4 GB total) of what seems to be the same memory? Also, if I am going to overclock the memory, is there a substantial reason to get the CAS 4 sticks over the CAS 5 sticks of what again seems to be the same DHX style memory, or am I really just spending money needlessly for the CAS 4 sticks?

I am going to do this on air but may explore liquid cooling as I've never gotten into that before either. I use the Asus Cool 'N Quiet technology to overclock as I am still acquiring this skill set, and I am hoping that there is a BIOS utility that will assist in OCing the RAM. So far, I have had good results with this method of OCing the CPU, and like the fact it throttles back when not being used. So far I've OCd two Phenom 2.6 quads, one Phenom 3.0 quad, one Phenom 3.2 quad, and now the 3.4. The 3.2 goes easily to about 3.8 without the blue screen and stays pretty cool, so I am interested in thoughts about liquid cooling and moving up to mid 4s with the 3.4, or even higher, as well as suggestions on overclocking using other utilities or even methods that the typical Asus board might support. Thanks.

Get the 8 GB pack as it's guaranteed at its specs, whereas 2 separate 4 GB packs when run together do not have the same guarantee as they are not tested or sold together.