I own the SVT-410HLF, and had use of an SVT-610HLF for over a month when my Mesa PH 610 was in for warranty work... IME, the SVT-610HLF is one of the worst 610s on the market... I *was* considering trading my PH 610 for that SVT-610HLF, only because it was lighter, and taller - therefor, easier to load into my truck than the Mesa... only problem was, the Ampeg 610 couldn't do the same job as my Mesa - it would fart out at much lower levels... I really felt that if I went that way, I'd be blowing drivers in the Ampeg in no time...
FWIW, I've been able to get the same job done with the PH 610, SVT-410HLF, SVT810e, Goliath Sr, and Peavey 215D-BW(KappaLFA loaded) - without stressing the drivers any... If you like lots of low end, DON'T get the Ampeg 610 - because it won't put out alot of lows... I can honestly say that if someone offered me an even trade right now - my SVT-410HLF(Nampeg) for a US SVT-610HLF, I would turn it down...
IMO, the 610HLF *tries* to be a compromise between their 410 and 810 - but fails all the way around: it lacks the physical size to be a ported 610...
YMMV, but those are my opinions/experiences...
- georgestrings