Had a spare hour this afternoon, so had a go at reusing a short SHS High-Speed motor with a long shaft armature from a 'generic' stock ferrite motor for giggles.
The results (so far) have impressed me - You basically end up with something like a 28TPA-ish High-Torque motor. A bit lethargic on 7.4v, but with an 11.1v it's got excellent trigger response, decent ROF (approx) 18-20rps with an 18:1 gear set, but runs very cool, which implies a low Amp draw.
It was definitely worth a punt. Just make sure you shim the armature to minimise shaft movement (oooh...errr!).