I own a Rectoverb and it's pretty versatile. Having said that, some days it sounds like **** and other days it blows me away. It must be atmospheric pressure as everything else is constant! I think some Mark users complain about the same thing. Strange..... anyway......
The clean pushed mode gives you crunch, ala ACDC, so to speak. It's a pretty versatile channel and I push it with a MI Audio Tubezone pedal for other tones and heavier drive. Sounds good. The 2nd ch can get as heavy as you want and you have 3 modes to play with (Series II Rectoverb only).
I can get heavy as hell tones, dark tones, bright tones, saturated tones, bluesy type tones, smooth lead tones.
Now, having said all that it's been a real b*itch to dial it in. On it's own, I find it cannot do. Most recto users use a tubescreamer type pedal, so do I. For good reason. I also use a MXR 10 band EQ in the loop... a must have.... and so do many other users. For good reason. Lead tones without some help?..... no way. Others may disagree. The amp on it's own just doesn't cut it for fluid type lead tones. It does need help. The Mark, I don't think you'll have trouble with.
I use a combination of pedals in front, namely a MI Audio Tubezone and Danelectro Daddy O and also a Zoom TriMetal and a Danelectro FishNChips EQ. With these pedals (one on, two or three on, EQ in/out) and control of guitar volume and tone control, I can get pretty much any tone I want, as stated earlier. I'm still experimenting with other OD pedals (have about 20 of 'em :shock: ) but at this stage this is my setup at home.
Now, as for the lead tones I don't think I can get to Mark type, but I think I can get 'reasonably' close. The drive/distortion character of both amps are different, so I don't expect the same. But I can get the sustain and smoothness that I require. Mark users say they get close to Recto tones, Recto users say they get close to Mark tones. Go figure.
My amp has JJ6L6's run in EL34 mode (yeah, I know......) but I feel it sounds better as the tubes run closer to their bias. I have a 5751 in V1 and the rest of the preamp tubes are JJ's. In a few weeks I'll experiment with different preamp tubes and get EL34's, too.
It's a difficult decision. Both amps are great in their own right. They have different tones and drive characteristics so you need to decide wihich suits you better for now and the future. I wouldn't want you to go and buy one based on what I said and then find it's not for you. These are my findings, I hope you understand that. You need to try, test and evaluate both amps. Youtube, at the very least, is a good place to start. You may find that the Mark suits you better.
Hope this helps.
PS. I was thinking of getting a Mark IV myself but I already own a Quad Pre and a 2:50 power amp, that I need to hook up.