I moved your screenshot to your post above. If your going to enter the contest you want your base score to be low and your overclocked gpu score to be high.
When you overclock it to run 3DMark 11 try turning off everything you don't need to run the system (Anti-virus, startup apps, etc...). I used to keep a list of everything I disabled so I didn't forget to turn it back on, but after doing this stuff a kazillion times I've got it memorized.
If you can do it and stay within the safe temps and voltage zones and you have it stable then... yea it is worth the time. Every little bit helps and plus OC'ing is fun
You won't see major improvements 100mhz at a time though. But I would guess your score of 3839 might jump to 3900. Maybe less of a jump. I am not sure. I know with 3dmark06 even the smallest increase made the score jump quite a bit because it was so cpu biased. Since 3dmark11 is still a synthetic benchmark I would imagine it would still be noticeable in the score.