I was debating what paint to use as well. Have used smooth hammerite on my last 3 cars with no issues. But with the ST I thought that because its so much heavier and has bigger discs and there is the possibility I might hoon down an alpine pass at some stage, that I'd get higher temp paint. So got a tin of halfrauds high temp engine paint in black. Still haven't got round to painting them though with all this cold weather.
I'd say if you going for a fancy colour then get hammerite as it has been tried and tested by many and the majority don't have any probs with it. If you're going for understated black like me, then might be worth getting high temp paint in the off-chance that hammerite might blister under heavy or frequent braking. Can't beat hammerite for easy coverage and good finish though.