If your engine is running o.k. with your present setup, don't change a thing. To my knowledge, there's not a chart or list that gives comparative heat ranges of different mfg's glow plugs, although it would be nice. Different engines have different performance,too and a plug that works well in one under a given circumstance may be completely different in another. It's a lot of trial and error, seeing what works best.

A 'hot" plug or "cold" plug is relative; one plug amy be hotter or colder than another. What determines this is how well a glow plug retains heat from one ignition cycle to another. A "hot plug will stay hotter than a "colder" plug, allowing for more reliable ignition (as in a 4-stroke, since the igniton occurs half as often at a given rpm), or earlier ignition, as part of the process is due to catalytic action of methanol and platinum, part due to plug heat, which actually "advances" ignition timing. Higher nitro content will also have this effect, because it lowers the flash point of the fuel, allowing it to ignite at a lower temperature.

You can see how changing things around can increase power, or can cause preignition or detonation, sometimes by doing the same thing in different circumstances. So, unless you are trying to hot rod, or fix a power delivery or an idle problem, if what you have now works, don't fix it.