I have a Mark IV, and it is a great amp. The COD does come close enough for me to not need it though. So it's a backup for the Egnater. I keep it because it's so versatile and cuts through a mix really well. Fairly compact, but the damn combo weighs more than my MOD 100 head, which weighs 65 pounds. Get the head if you want the IV, your back will thank you.
The V sounds great on the vids, but I just don't see the point. The IV's only weakness that I find is channel 1 & 2 share the mid and bass pots so you compromise there. But the channels are so different you can easily find a happy medium. One other small thing is the lead sound has a midrange honk that you can't dial out. But that's the signature sound.