I'd go with the GMT which supports the DDR3.
I'd go with the DDR3 RAM. As you say, the price is about the same.
DDR2 can clock at 1066MHz where the DDR3 can clock at 1600MHz.
A blind man could see which is the better clocked version of RAM.
Also, on average, DDR2 operate on a slightly higher voltage than the DDR3 which by definition means the DDR2 will run hotter than the DDR3.
The less heat you generate, the less heat you have to get rid of.
And, all the DDR3 strips I've seen have Heat Shreaders and that is a good thing.
Well, that is my opinion and I'm stuck with it.
FYI - I assembled my system and I have 12GB of DDR3 RAM.
So, you might say I practice what I speak.
Good luck with your new system. May it work the first time you turn it on.