Yeah, the P2 is a very cool chip indeed but it does not run cool. Some say it runs hot. Wot then is hot?
Let's check it out with a P2D2 that I have mounted flipped with the chip facing down and a thermocouple taped with polyimide to the rear of the pcb smack bang center of the P2 hotspot. My bench P1 reports the ambient as 26.7'C with 55% RH in still air, no fans or A/C etc.
Now I will test the P2 using a new version of TAQOZ that has VGA and a keyboard connected as well as other devices. I am mainly using two cogs, one for TAQOZ and one for 640x480x8 VGA and the TAQOZ console is switched over to VGA and keyboard displaying text and bmp graphics etc. The 12MHz clock divider is set to 1 and I am multiplying from there.
>5 mins FINGER >2 mins
NO COOLING TOUCH 25mm FAN NOTES
100MHZ 43'C 33'C
120MHZ 45'C 36'C slow to heat
180MHZ 54'C 47'C 39'C
240MHZ 59'C 50'C 40'C
300MHZ 63'C 52'C 43'C
324MHZ 66'C 55'C 44'C burns my finger
So I wouldn't operate the P2 at 300MHz without cooling unless it was used indoors where the ambient is low but by the same token even a tiny bit of heatsinking with my finger will immediately cool it and even using a very small 25mm fan will prevent it from ever feeling hot to the touch even at 324MHz. When I get some new chips during the week I will check one out on the current P2D2 before deciding if I want to add extra layers. My opinion is that I don't need extra thermal layers, but if run at 300MHz or so I just need a tiny bit of air flow or place the back of the P2D2 against a metal case.
BTW - activating all the cogs doesn't really seem to make much difference.