So I actually put the cab up for sale after reading all the pros and cons, I did an A/B test between the ENGL cab and my Marshall 412 and decided that the JCM 800 cab does what I need for now very well. The G12-65 Celestions sound amazing for Hard Rock and Thrash and have more of an old school vibe, the ENGL cab sounds deeper and fatter but I actually like the more biting nature of the Marshall 412.I sent Lasse Lammert (German Metal producer) an E-Mail inquiring about the swapping of speakers since he did exactly what I intended to do, his response was that the V30 do improve the sound of the standard cab but the "real deal" still sounds tighter. So I'll just stick with my Marshall cab for now and keep my eyes open for a decent used V30 box.Thanks for all the input, I'm sure this thread will help out a few people who have the same questions as I did