My Pi is giving an average of 2.33 on MinePeon, with an average of 2.24 at the pool. No special mods, no special drivers, just:- -S BPM:all
Reject rate is 0.81% HW Error rate is 59.23%
simple maths says this is not a true error rate.
2.33Gh less 0.81% = 2.311Gh The pool shows 2.24Gh so corrected HW error rate must be 3.07%
The extra 56.16% is probably down to running a 5Gh chip at less than 2.5Gh.
So with 2.24Gh at the pool I am quite happy for now.
In short ignore the HW error rate, Its not true. The actual figure reported at the pool is the one that pays you.