That seems a tad high. However I don't think there's a chart specifically, because really it varies between machines and personal preference. Some people can't stand to see anything higher than 40C. Some CPUs are also simply more stable at a higher temperature than others, because not every core out of the batch is perfectly the same.
What kind of cooling are you using? What's the 1.6 got? Does one case have better ventilation than the other? Your rig shows you've got the CPU overclocked to 2.8GHz, so you should be comparing temperatures to a 2.8GHz P4, not a 2.4. Did you increase the CPU voltage to get it to that speed?