So, long(ish) story short, I switched from an 850 watt psu (not sure about brand or model) to a Corsair AX750. Full specs are:
Intel i5 2500k, Stock cooler and no overclocking.
Asus P67 Sabertooth
4GB Corsair Vengeance
MSI Twin Frozr III GTX 570 (Also running slightly hotter than usual, thought not as much as the cpu is)
Seagate Barracuda 1TB
Intel 320 series 120GB SSD
WD Elements external HDD, permanently connected
The aforementioned Corsair AX750.
After installing the new PSU, temps jumped from around 35C to 40-44 C at idle. I was mostly just wondering if the reduced power availability would result in higher temps.