That riding condtition (slow traffic / hot weather ) is exactly what I figured you meant. I believe the Jardines do help. I've had them for a few years now. I've had the stock exhaust, TORs/cat bypass, and settled on Jardines after I heard Britman's bike at RAA III..
However, they are much louder than the TORs. I love the sound of them though and they are not nearly as loud as most of the HDs at our local bike night.
Also.. I don't know if you run a windshield like the Roadster screen or not, but that sucker traps a butt load of heat at a stop that comes up from the radiator. I run the fly screen year round, but I tried the Roadster screen for a while and couldn't deal with the heat at a stand still. I'm not a windshield guy anyway.. I just run the fly screen year round.