The Q9650 is pretty old while the i5 is VERY new, what are you planning on doing?
Upgrade to a 3450 from a Q9650? Not really worth it, as the Q9650 was one of the best 45nm chips during it's time. It's still very comparable to a modern day i5. A good upgrade would be waiting until Haswell, which is coming out next year.
If it was in the same generation, it would mean a little, but the i5 3450 is a much better and faster CPU overall.
This isn't an exact comparison because it's a 2500K (about the same performance at stock as the 3450 because of the 3450's slightly better per clock performance, despite a slower clock speed) against the Q9650, but it gets the point across. http://www.anandtech.com/bench/Product/49?vs=288
I DO agree with amuffin, though, if you already have the Q9650, just wait for Haswell.