Had mine for about a week, but have only been isolated to individual testing (didn't have practice last week). I've run a few different tests all at low to moderate volume. I haven't noticed any unusual behavior. But I have NOT run this at any volume for a few hours.
My testing/practice has used a 1x12 Avatar and a 2x12 Avatar cab. I have an American Jazz, Thunderbird Studio and a Peavey Zodiac DE (PJ). For testing the amp I didn't use my Line 6.
Tone: it's all about the tone. Tone is a very personal issue but the SVT-7 is the tone I've been looking for. Keep in mind that I primarily play hard rock, alternative rock, heavy-alternative, and some metal. So, I'm very focused on a tone that has a lot of bottom and mids, with some overdrive that is still 'warm'. By way of comparison I have had an Ampeg SVT-350, Markbass LMII, Ampeg BA500 (combo), Markbass CMD 121 (combo), Workingmans 4004, and an Ampeg B2RE. Those are my primary points of comparison. Unfortunately I can't directly compare the 7 to other PRO series (some GC experience but thats all). The SVT-7 is by far the best of this limited lot. Again, the tone characteristics of this amp are really hitting home for me. I was able to quickly dial in a very nice tone that was warm, but still able to overdrive the tube pre for some grind. It seems to be more mid-focused than the LMII with a better overdriven sound (product of the tube pre). The tone is much warmer than both the B2re and the 4004 and not hi-fi.
The controls are simple and straight-forward. The compressor is very good IMO. Very usable and helped give me a nice even tone without destroying the lows or highs. I like the mute switch that Ampeg uses on most of it's heads and this will no doubt be a well used feature when in practice and out. The PAD really drops the volume. I use all passive basses (though all have very hot pups) but I don't see me using the PAD feature. The ultra hi and ultra low are a nice option and a very usable feature. I have practiced with both switches on. Again, I haven't test this at any volume for any length of time so I'm not sure yet if it starts to cut out or crap out at higher volumes. The mid selector is a nice feature but I haven't noticed a tremendous impact to the tone. It helps dial in the mids, but I was quickly able to find my setting and didn't thoroughly test the settings.
I think the aesthetics and and simplicity of the SVT-7 have been commented already and I would agree. It's a nice simple, easy to use amp. Its noticeably larger and heavier than the Markbass head, but still one of the smallest and lightest amps I've had. Its has a very solid feel to it and doesn't seem like you could shake it off your cab :-D
Power wise, it has plenty of headroom for what I do but not sure of the 1000w claim but it can definitely crank and it's clean and clear up to the higher volumes. As I said I can't make any comments on the volume and tone in the mix, but it's been great to now.