I'm RAMmed with confusion =\

I'm in the process of spec'ing out a new system. I haven't built a system since the P4 days.

I'm looking at the AMD Phenom II X2 550 BE as my CPU of choice since I haven't read anything that indicates Intel has a CPU with as much bang for the buck, potential un-lockable cores and ability for a pretty high OC (600MHz+ I've read from some).

I am also looking to run on-board video GPU until I can afford a dedicated card. So, I've spec'ed either the:

Gigabyte GA-MA785GM-US2H (DDR2 1.8-2.1 compatible)

or the DDR3 version: GA-MA785GMT-UD2H

Now, my quandary is on selecting 4Gigs of memory for what I do:

1. Plan to OC in the future to raise performance/dollar
2. Run a pretty intensive flight simulator (RealFlight G4.5)
3. Run Photoshop and occassionally have some pretty darn big files to process (average around 1gig in file size sometimes)
4. General computing (web surfing, email, word, etc.)

So, sifting through NewEgg's site I've found all kinds of numbers that cause me uncertainty. For DDR2, I find that the lower voltage RAM (1.8) tends to be more expensive than the higher voltage stuff (2.1). Same on DDR3 side.

I am confused and uncertain on what speed RAM to go with, whether it be DDR2 or 3.

While I don't suspect all traces of DDR2 to disappear in 2-3 years, I'd like this computer to be about to be upgraded. From what I've read, the current crop of AMD processors don't really do as well as they could with the DDR3 technology, obviously something that may improve over time.

When it comes to a difference of $20-$30 to go from a DDR2 setup to DDR3 with the potential for further performance increases, then I'll go DDR3. However, if I can get equivalent performance with DDR2 for less money, then I'd like to save that money!

My last computer held up well for 6 years with some minor upgrades. I was able to run my simulator and photoshop without too much headache on 1gig of RAM lol  

Any insight or direction would be greatly appreciated! Also, while rebates are nice, I'd like to pay as little upfront as possible.