My 2.53b at stock idled at 35c and load was 55c with stock heatsink / as5, but currently it is at 2.87 with a Zalman 7000 AL CU / as5 and idles at 33c loads at 56c. Hope that helps
Man, a 4c temperature delta is pretty awesome. Sounds like you have excellent case cooling. Those temps are fine, but if you did use a better HSF you would get lower idle temps for sure, but unless you are concerned about noise of the stock HSF (I suspect you are not since you obviously have lots of ventilation already) I wouldn't worry about it.
The idle temp looks too high to me, and as noted above that's a very low delta between idle and loaded temps. Are you sure you're getting a correct reading?