i've had a Mark V since June but my Ecstasy only a month. so i can't give a definitive comparison, but i can give some impressions.
i dig the Mark V. the cleans are gorgeous--better than the Ecstasy IMO, although with bright preamp tubes i can get the Ecstasy close. the Mark V has more clean versatility with its three modes, one of which is a nice SRV sorta "pushed" clean tone.
the Mark V gain channels all have that dark thick Boogie sound. the Crunch channel i find really balanced, good lows and highs, and gets up to medium-high gain. the Mk IIC+ mode has less lows and not super-high amounts of gain but has that 80s LA metal bite to it. the Mk IV mode is darker with more lows and more gain. the Extreme mode is like two-thirds Mark plus one-third Recto--mean and tight. the Mk I mode can be boomy but dialed in right is very thick and creamy--classic Boogie lead.
in my time with the Ecstasy gain channels so far, it sounds more snarly, more EL34 mids sorta sound, than the V. it's still plenty thick but a slightly different sort of thick, a bit more open and less dark. i think it's somewhere between the dark Boogie sound and the raspy higher-mid snarl of the classic Marshall sound--snarly but a bit dark, if that makes sense.
the Ecstasy is less tight for me in the low-end on high-gain sounds, and has a bit less low end than i'm getting from my V, but that may be because i haven't dialed the Ecstasy in great yet. (it's also part of the reason i want to try KT77s in my Ecstasy, to get a tiny bit more of that 6L6 sorta sound, slightly tighter and bigger low-end.)
they both have lots of switches and options for tweaking, which is cool. they both have half-power options. the V took me 8 months to dial in right, preamp tubes and settings. but i've heard the Ecstasy can take a while too. i haven't yet gotten a great smooth lead sound out of the Ecstasy, but Steve Vai has, so i'm pretty sure it's in there.
