My 5670 overclocked can hash at about 110MH/s max. Since the 6670 have 80 SP more, its hash rate is probably between 120-135.
They're not the same SP's. Efficiency for mining for the 6xxx series is a bit lower IIRC.
Even with the 3% bonus and such, a 900MHz (over 800MHz) 6670 won't push much past 110mhash/s
Even if the hash rate per SP is not the same, considering that the 6670 have 80 SPs more than the 5670, the total hash rate difference will be more than 10MH/s.
If we were comparing a 4000 and 5000 series, the hash rate per SP difference is almost 2x. The difference in hash rate per SP between the 5000 and 6000 series (excluding the 5700 and 6700 series, same cards but tweaked a little) is very small.