Yep, never heard even one report of low horsepower before that BGM article. It was in fact quite the opposite, with people reporting how it was trouncing their favorite 500 watt micro. TB is so fickle and hypocritical when it comes to things like this.
The RH750 is much punchier than the RH450 because of that extra headroom. It also is able to better utilize the power via the APM technology which makes this head what it is. But in the case of the OP, it wouldn't give you a lot more volume through a single 210, though it would definitely feel more "willing" and lively then the 450 does. Adding a second RS210 is the easiest way to have your same sound, only much louder.
The RH750 is much punchier than the RH450 because of that extra headroom. It also is able to better utilize the power via the APM technology which makes this head what it is. But in the case of the OP, it wouldn't give you a lot more volume through a single 210, though it would definitely feel more "willing" and lively then the 450 does. Adding a second RS210 is the easiest way to have your same sound, only much louder.