To all those mappers out there, feeling the pain of those long compile times even on good PCs. It was never your fault! Blame Volvo. ):
Turns out a intersection tracker in the raytracing code for VRAD was decreasing performance the more threads you had due to poor multi-threading programming knowledge??? Jokes this was obviously a mistake but still the performance hit is abysmal and this bug was in VRAD for years without anyone knowing until now.