I am the owner of a STL900 and the RH750.
...Too many people think in bubbles and sit and analyse amp specs. You know what, get gigging and forget about it. If the amp underperforms at the gig, I then understand the frustration, but the RH450/750 will always be known, to me, as massively loud.
...The STL900 is a very very loud amplifier, more than I need, but again, I bet if you measured it under a certain system, it wouldnt be 900W RMS...and thats not a poke at GB ether, because this amp SLAMS...completely.
+1
I sometimes wish that dB and power ratios worked on a linear basis instead of logarithmic, simply because so many people misunderstand them.
First off, unless you have some pretty impressive cabs, you can't experience the full potential impact of an amp like the SL900, because your cabs will start to compress well before the amp hits its full power rating.
Besides, even if you have the Cabs Of Doom, a difference of a few watts (or even a few hundred, in some cases), simply doesn't matter. The conventional spacing between the lines on a volume knob (or beside the faders on a mixer) is 3dB. Any time I've been on a gig and felt like my amp was underpowered, I've needed more than just one line on the fader, and if the power ratings on both Streamliners are perfectly accurate, the difference between the 600 and 900 is only roughly half a line.
Some interesting examples of relative power output, expressed as a dB difference (assuming that everyone's ratings are accurate):
Markbass LMIII vs SWR Headlite = 0.45dB louder
Genz Streamliner 600 vs Markbass LMIII = 0.79dB
Streamliner 900 vs 600 = 1.76dB*
Streamliner 900 vs Markbass LMIII = 2.5dB
TC RH450 (marketed) vs TC RH450 (actual) = 2.79dB**
Streamliner 600 vs Mesa Walkabout = 3.0dB
*Unless Genz worked more magic in the 3DPM circuit on the 900, in which case, the subjective difference between the two could feel like 3dB, 6dB, or ???
**That is, assuming you only use the TC to play continuous tones from a sine-wave generator, instead of using it for bass guitar. Like, say, an actual musician?
Secondly, the convention of naming amps according to their power output is nothing more than a marketing convenience. I expect that the only reason that Genz called our favourite amp a Streamliner 900, is because SL 927 (or SL 853, for that matter) wouldn't have much of a ring to it. Is anybody really clueless enough to believe that a "50-watt" Marshall guitar amp actually puts out 50 clean watts, or that the Streamliner 600 and 900 BOTH just happen to max out at perfect round numbers? Sadly, the answer seems to be "yes".
More importantly, when it comes to the highly subjective thing we call "loudness", voicing, breakup at the limit, and other factors matter far more than wattage. An amp with a wide, relatively flat voicing like an Eden, won't sound as loud as one with a more tailored, peaky response like a G-K. An SVT will happily go much louder than a conventional solid state head of the same advertised wattage, simply because the SVT continues to sound good when it's deep into the breakup zone. And an amp that's hampered by a poorly-designed compressor like the Eden WTX260, won't sound nearly as dynamic as its power rating suggests.
I actually feel for TC Electronic. They built an affordable, lightweight SVT-killer, and the clever power management makes it sound far louder than its continuous RMS power. Knowing that their target market is working musicians and hobbyists rather than audio engineers, they must have lost a lot of sleep figuring out how to market it. How do you explain a solid-state amp that slams as though it's an all-tube lead-sled, in a world where customers are so uninformed that they give SWR heck for rating the Headlite at "only" 400 watts, instead of going for the "full" 500?
By the way, I chose the manufacturers in my dB comparison specifically because NONE of them, including Genz, rate their amps according to hi-fi convention. Check the websites for yourself: they all use rounded off power "ratings", with no qualifiers for % distortion or frequency bandwidth. No-one beefs about their ratings, for the simple reason that their amps sound great, and are #$&@@!!! loud for their size. Just like the TC.
IMO, some of the guys over on the TC RH thread have been acting like schoolgirls. I really don't care how accurate the power rating on my Streamliner 900 is. It's louder than any sensible person needs, and I bet an RH750 is, too.
The way I see it, if you like the features and processing on the TC and are comfortable with their customer service record, then buy it. If you prefer the sound of the Genz and want to experience their stellar customer service, then buy the Streamliner. But whichever amp you choose, use your ears as your main evaluation tool, not a poorly-understood spec sheet.
sounds great to me with my STM-900 and P5. 
