NO a gtx 470 is more then a little faster then a 5850 and is much faster when both are overclocked.
GTX overclock scaling is better then the 58xx series.
A overclocked gtx470 = gtx 480 give or take
A overclocked 5850 = a 5870 give or take
A overclocked 5870 = gtx 480 give or take
A gtx 470 is a full 10% faster then a 5850 at stock allready, and sometimes beats a 5870.
Based on computerbase the 470 is (-2)-9% faster without AA depending on resolution and 3-16% faster with AA. So for a $190 470 vs. a $175 5850 the 470 averaged 7.75% faster (I classify sub 10% as a little) and 8.6% more expensive. Again, I'll take the cheaper one with those differences.