I've been running my rig catless for a while now and would like to say it helps with the heat but honestly, I can't tell a difference.
+1 on that. I can't tell the difference with the cat out. It still burns your thigh when yo are in traffic and is very warm at 60 miles an hour. I did noice the sound was a little better when I removed the cat but not the heat.
Went catless (stock headpipes) a couple weeks ago and it is cooler but still hot. Just not as hot. Going with Mobil 1 Synthetic (Got Syn 3 Now) and a low temp thermostat to try to cool it down more. May also go with an ViED as well. Have stock intake and mufflers.