Srwooten
it's as good as any I suppose. Not too many makers publish their power reserve capacities thoroughly IMO.
I sought merely to broaden the viewpoint by injecting some other facts. interjecting there are more criteria to this than noting if amps double up their outputs if speaker imp halves.
As fair a rule as is that, I've found with conventional transformer coupled output amps, I look at the over all weight... now. it indicates to me a general rule of thumb that serves me pretty good, as it speaks about the build of the amps power supplies most often. great amps have great power supplies more often than not.
Also the weight of an amp is not a physical worry for me, usually. It is for some I'm sure.
Voice, input impedance, topology, power reserves, negative feedback or no, are important things I look at when deciding on amplification. To buy an amp however it may not meet my expectations in those regards.
My latest amp acquisition for ex, meets but a few of my short list desires for what an amp needs. it's not heavy, doesn't have enormous power resivoirs and isn't my typical choice of transformer coupled output. In fact it is dainty IMO by my usual amp standards, but the sound and performance exceeded my expectations. A lot. it's price exceeded my predetermined budget too! IMO that's usually what happens to me though.
it's not eye candy either until energized and the lights are off. otherwise it's pretty plain and sort of dull looking as amps go. It's my first 'hybrid' amp too.
I was avidly seeking out an ATI amp for the last few months and a couple others. I almost pulled the trigger twice but both deals weren't quite to my own personal needs. Or this new TDB 5150 wouldn't have gotten here at all.
Hope that helps clear things up.