Some chips are better than others. I know that mine's very average. I'm stress-testing it again right now for the first time since I added my 2nd GTX and I'm having to feed 1.475v just to get her to 3.5 stable.
But your temps sound decent. You'll probably want to keep your FSB @ 400 or under on your P5B. It has a chipset strap which loosens up timings once you go over that and decreases overall performance slightly. So go with a higher multiplier if you can.
The issue was covered in great detail here: