The 30 amp ESC's will do the job for a 2WD machine with batterydrills.
But once you go for more power,like using Ranglebox Saturns, or the old style Groupner Speed 900 it will get iffy.

The Tz85's have proven to be rock solid, so I would suggest to bite the bullet.

It's also easier to find replacements during life events, as a lot of UK feathers use the 85's.