I've owned the Model's 1,10 and 501. the 501 is the better of the 3 in every respect.
Conventional wisdom various owners that I know (incl. myself) is that the 10 and 12 kick butt over the 201/501 series in a big way. the 8/9 series was pretty well regarded, on par with the 10/12 at least I'd think. 8's with the BPS would be pretty righteous, but a lot bigger and more power hungry than a pair of 12s. I have a 10, which I prefer to the 201/501 series.
As an owner of an original Model 8 with choke power supply, I found it far superior to the model 201 I heard, at least IMHO. Have not heard the 501 so cannot say, but the 201 was not in the same league as my 8. The 201 was far less resolving and seemed much less powerful with restricted dynamics and loss of focus at both ends of the frequency.