I'd say the 175 is better.
I'd say that a lot depends on your other hardware. My 175 won't go anywhere but stock (won't even do a variation of stock like 10 * 220 VS stock (11 * 200)). This with Corsair XMS PC4000 (2 * 1GB). I suspect my MB may be the culprit - MSI K8Neo4 Platinum.
My point here is that if your hardware is capable, the 170 should be fine. If your hardward isn't, then the 175 is faster at stock than the 170. Both are quite excellent CPUs however.