CPU too hot?

I have 2 machines, both using the same Athlon chips - XP 2600+ 333 FSB, with
DDR333 ram. Different brands of motherboards & cases, etc. Utilizing a
little program called "WCPUID", both chips appear to be identical in specs
(AMD 2600+ model 8, etc.)

My problem, assuming it is one, is this: one CPU maintains a much higher
temperature than the other, yet it's board temp is cooler. Using two
different monitoring utilities, SiSoft Sandra and Asus Probe, I note the
following temps:

Machine # 1
CPU - 60 degrees (c) at idle; 65c stressed.
Board - 36c
(the same approximate temps are given in the BIOS)

Machine # 2
CPU - 40c idle; 44c stressed
Board - 46c
(Note: the BIOS shows the CPU to be 54c ???)


Strange, to me anyway, is the fact that the system with the higher-temp CPU
has the coolest board. (both cases have front & rear "push-pull" fan
arrangements.)

Machine # 1 has a new Thermaltake heatsink and fan which is rated for XP
3100. I don't remember what # 2 has. Both heatsinks were installed using
thermal grease.

Also of interest may be the fact that the mobo in #1 (an ECS L7VTA) is
supposed to recognize the CPU and set the FSB accordingly. Yet it
identified the chip as a much lesser model, and defaulted to 100 MHz. I
jumpered the board to run at 166 MHz (x2) to obtain the XP's 333 spec. I've
run extended stress tests, and the system is very stable.

Although AMD rates these chips for a max. operating temp of 85c, I'm
concerned that 64c will shorten the life of #1.

Any comments or suggestions will be appreciated!