By way of an update, I took this to a rehearsal the other night, in a large room, at pretty much gig volumes. The amp performed without issue, and sounded bloody great with my '73 P - huge tonal range just from the passive tone control, but I needed to back off the bass a bit because I was runnng through my BF Super Twin. When I kicked in with the Em riff of Steely Dan's 'FM' I got a big smile and a 'yeah' from the guitarist whose band it was!
I'm rehearsing with them again next week and I'm going to take my Dingwall NG2 as well and see how that sounds (although I can kind of guess).
I was trying to work out what it cost me - I'd say about £500 overall, not counting my time of course!