I'd keep the 9mm, 30mm and possibly the 6mm. The 9mm is right at the 2mm exit pupil sweet spot. The TMB (unless it's a SuperMono) probably won't fetch much, so you might as well keep it for a little extra power when conditions permit - it still won't be very high power. Re the 42mm you might be told, or read, that it gives too big an exit pupil in your fast newt and the view will somehow be inferior.
While that is bollocks, you might still find it to be of little use simply because you have the 82°30, which will give a similar TFOV at higher power and similar brightness.