3DMark score by 200 can be significant, or insignificant. If you already have in excess of 10k score, 200 might just be luck.
You should try running it 10 times on OC, and 10 times on the slower speed, and compare min and average scores. That would tell for sure if its a real change.
Also, you might try SuperPi, which would need fast RAM as well (I think), or some mem benchmarks (Everest does that). Again, run it multiple times, and review min and average to see if its a real change.
Or you can just sit back, and be sure that even if its not any faster, it definately isn't any slower.