But what I still dont understand is where TjMax can be read from.
AFAIK Realtemp uses MSR 0x1A2, for approximating temperature, when available. alex98uk you could check this MSR if you want to confirm, perhaps something like a cpu-z or hwmonitor dump will tell you. You might see something like
MSR 0x000001A2 0x00000000 0x00641400
where the 64 would be your target temp or Tjmax in hex. The decimal equivalent of 0x64 being 100, so Tjmax would be 100C.
Don't know about the PECI stuff as I haven't come across any PECI hardware. Maybe someone on the board has it. AFAIK it should show a running average of the hottest core from PROCHOT, or is it target temperature or Tjmax hehe. I think they are all more or less the same thing