it's if your a cord guy or not a cord guy...
If you like the cord -> mx510
If you hate the cord -> mx1000
mx510 is one of the best corded mice out there for gaming.
mx1000 _IS_ the best cordless mice out there for anything including gaming.
For me, the cord gets in the way more then naught.
In regards to precision, a lot of review sites say that the mx510 is not as precise as the mx1000.
However, the thing that deters people from mx1000 is that some of them are buggy. My mx1000 does not have a lag time nor does it turn off when I lift it.
Also, the amount of time it takes to get used to the precision takes about 2 weeks. It's an excellent mouse.