As others said, Q6700 has a higher clock speed, and given that it's the same family, you're better off getting that one.
However, upgrading to a five year old CPU may not be the best move.
If I were you, I'd get a brand new Pentium G620 for $65, a cheap LGA1155 motherboard for $50, and 4gig of ddr3 for $20
That way you'll have a new, upgradeable machine that has warranty, that uses a lot less power than Q6700 and beats it in most benchmarks (also has integrated graphics if it means something to you).
Of course, that's $135, not $100, so that may not be an option for you. Also, assuming you're in the US.