R has more phases than the L as well as a larger heat sink on the north bridge. At least it did when I looked at these two boards a while back. I ended up going with the R paired with a Q6600 but be aware, it has significant vdroop so extreme overclocking isn't going to happen. It's fine for light to moderate clocks though.
Did you purchase the P35C version? I have the GA-P35C-DS3R and have been happy with it as a non overclocker (just recently started acting up but a new CMOS battery solved the issues.) However, I seem to recall reports at the time I purchased it that the P35C version didn't overclock as well due to the compromises made to support two types of memory.