I'm also getting HW errors over 10% even when using a shielded alternative USB cable. For example, my latest run (int:52:2:950) has been going on for 70 minutes and the CGMiner reports:
DRB 0: E8 34 max 34.8 | 22.60G/19.87Gh/s | A:18954 R:24 HW:2233 WU:277.4/m
Those hashrate seems good you can also try 53:2:950, us cgwatcher to monitor. you must have fan(s) on the heatsink and also a fan on the other side also helps
I'm trying 53:2:950 right now actually. I have fans on the heatsink side (the big silver one with no components) only right now. I didn't think 35c was too hot.
What concerns me is the high HW rate though. Over 10% seems more than most people are reporting.