I'm not sure on that. Look at what sidehack was able to do with a chip. I mean it's able to do 8GH easily with no issues.
While the Compac will run passive at 8Gh/s, I wouldn't really recommend it - never mind if putting it into an enclosed space with limited surface area for cooling (which the R1 largely appears to be, ventilation holes notwithstanding).
I was surprised how hot the heat sink got when running a compac at only 125 freq, I put a fan on the one I have at that frequency right away after I touched it.
You might try to turn down voltage and see if it makes a difference. What speed are you getting at 125?
I have 2 at 150 and it ran fine with no fan. Now the ones I have cranked up to 250 I had to add fans. They really did get hot, but well within spec.