i have to say that I generally concur with Bigwan here.
The reason I went for the Terror is because, after borrowing one for a few gigs, I found its 'flat' sound very similar (not exactly the same) to the Ashdown with the settings I used....again, more valve than not, mostly flat with a touch of mid. The Ashdowns generally tone is a little rounder and a bit more 'complex' sounding, but then in the Mix you don't really notice.
The Orange is famously weak in the EQ section, but then the Flat sound is great to my ears, so I don't care.
It is VERY loud for what it is, but having said that, the hi-gain stock tubes mean that it can run into light overdrive fairly easily (no bad thing if you like a bit of grind), but it renders the DI out useless. I, along with many others here, changed the tubes for slightly lower gain ones to give more useable clean volume.....for me though, it didn't really fix the rediculously high output on the DI. I'm not fussed about the DI issue as I'll generally use a Sansamp if I'm DI'ing.
All in all, they compliment each other really well I think, if you're doing a small gig and don't wanna lug the Ashdown out, the Orange won't disappoint
Si