The mk2a has a bigger cache than the mk2, and will hence cache more.

2.0 betas will run cooler than 1.x as the caching code was improved, hence the drives spin up less often and stay spinning for less time.

There weren't any other circuitry changes between the mk2/mk2a that would make a difference to heat - just more ram (in fewer chips) on the mk2a - but RAM runs cold anyway.

Hugo