I got my Healey after several years of MGBs, and always adjusted their valves at .015" cold, as per the manuals (all in agreement). Seeing that the Healey was calling for .012" hot, I compared the settings under both conditions.
The conclusion was that .012" hot was the same as .015" cold.
Just remember: loose valves won't cost you money; tight ones will!
The only "cooling" an exhaust valve gets, is the time it can dissipate heat while touching the seat. A tighter setting minimizes the time spent on the seat. The intake valve gets a nice cool charge across it every time it opens, while the exhaust valve gets doused with 1375 degree spent gasses (assuming a correct mixture; even hotter if you're on the lean side) each time it opens.
Give the poor exhaust valve a break, and set them all at .015" cold.
Edit: aftermarket cams (like my 3/4 Isky) generally require even looser clearances; mine are .018" intake/.020" exhaust.