I don't think bus width, in itself, directly affects memory chip temps. But a wider bus width will take more PCB area and, depending on the design, may lead to less component crowding giving lower temps.
Or may not.
According to some reviews and forums GDDR3 doesn't have problems with heat. I guessing in the case I listed the persons GPU chip produced large amounts of heat over stock. The 9800m GS was practically a down clocked 9600 GT. 9600 GT's have a 50% greater TDP than HD 6670's which is what my gpu is based on. I going to say that overclocking the card made the ambient temperatures really hot which then overheated his memory.
I read in 6970 review that it could limit its TDP to prevent overheating even under furmark with a large a overclock. If my 6650m, which is based on the 6670, has this feature it might mean that the gpu will never go over it TDP specifications. The could mean that the ambient temperatures will never go over the manufacturers expectations even if I overclock it. I just need to find out if the lower end 6000 series cards that are not rebranded 5000 series cards have this feature.