How comfortable is the Raven compared to the MTAC as a IWB holster?
I can't speak to the MTAC. I switched from a Milt Sparks SSII to the Phantom a few years ago. I wear IWB almost exclusively. I found that, with my 5" 1911, I no longer had to go up a pants size for IWB.
Of course, I carry on a good gun belt, as you should too. No, not the best "heavy duty" belt you can find, a belt designed for supporting a firearm.