If you're doing nothing but speed runs for 10 minutes straight, it could be that you are over-revving the motor...

I don't have any experience with REAL 540 cans in this truck....ran a Mabuchi 540RS to break it in, but that was it.... Also, my buddy was running a Novak 5.5T 550 in it, and his temps were "really high' during practice....until the race director talked to him and noticed that he was running 18-20 minutes straight....which will add a lot more heat than a 5 minutes qualifier or 7 minute main....

I say, get it on a real track and even if it is in practice, find out how long they run their mains for, and set a timer for that length of time....go and finish your last lap after your timer expires, then run down off the stand and temp the motor.... 200+ after 10 minutes might only be 170 after 7 and 160 after 5 and you might be OK...

Also, Krio is right, that super high traction will add a lot of temps too. We were running 14/62 on short grass and getting 150+ temps on our 550s...once I got it on the clay track, I was able to gear it up to 16/62 and was still barely hitting 150 in the mains.