After owning all the Mark series amps from the IIC+ up to the V, i have a Fortin modded Marshall and it really makes me smile everytime i plug in. If you love the Mark series amp you can dial in tones on the Cali mod that would make John Sykes proud, but you can also dial in brown Marshall tones with much less compression.
As far as Boogies go, i disagree somewhat about the III sounding dead on with the IIC+'s. I've owned them both and played IIC+ amps in the same room as Mark III's, blue stripes though. If anything the III's have more gain but they sound nasty compared to a IIC+. The IIC+ will sound warmer, more organic, without the harsh top end all IMHO. Of course you can dial in III's to sound how you want, and i believe there's some MOJO in those coliseum amps that makes them sound better than a regular III.
And the Mark V....yeah, forget that amp, not close. The Mark V sounds like a more vanilla version of the Mark IV with less gain.