A cam and/or a 30t sprocket won't do anything to lower the temp. An oil cooler or fan could help, but Cat-less pipes and a TTS with a good map or dynotune will do more to help performance and temp than anything.
I have a 30t sprocket, and there are trade offs. You do get a little more low speed umph, but it will also increase your rpms at highway cruising speeds by a couple hundred rpms. It's very noticeable here on SoCal freeways where traffic is always going 75+ (or 0). Also, it alters the calibration of the speedo, so you'll need a good programer like the TTS to recalibrate your speedometer.
The 255 is a great cam for low end. Somebody here had a thread about keeping the 255 and machining it and modifying the motor to get great numbers and keep the bottom end of the 255. From Canada, I think. Anyway i think that would be a good option.
Good luck, I'm sure you'll be happy with whatever you choose.
Dan