There is a lot of differing info on which primers are hotter then others. From what I learned, that is not the main issue.

I stumbled over a research paper on primers once that cleared things up a bit for me: The researcher took pictures of the ignition flames and you could clearly see that Fed 215 and CCI 250 were related (short, but broad-based flame) while WLRM and RWS 5333 were related as well (long, thin flame). And in deed, at least in my caliber, I could substitute Fed 215 / CCI 250 and WLRM /RWS 5333 with almost no difference in results. The heat of the primer does not seem to be the only issue, but also shape and duration of flame. As particular powders react differently, especially across various case geometries, the heat of a primer per se cannot be the only concern - hence, one has to actually test what works best, and that may be a cooler primer.

Another research paper on primers plotted pressure and velocity as caused by various primers against ambient temperature, utilizing various powders. These were standard primers as well as magnum primers. At higher temperatures, the differences the primers made were very small and largely powder dependent. Only at lower temperatures did primer performance show large variations independent from the used powders. Interestingly, the Fed 215 was the only primer that kept its ignition power well into 'cold' territory, all others dropped of steeply as 0 degrees Celsius was approached. At 40 degrees Celsius, all primers showed more or less the same performance.