Nice looking bike.
The TT600RE has the engine from a 1990-1995 XT600E.
From memory, the TTR600 has:
A lighter crankshaft.
Narrower engine by about 30mm
Different internal gearing (gearbox)
CDI ignition vs TCI, and possible “wire mod” for more power.
You already know all about the suspension and the rear wheel.
I don't really remember the difference in power/torque since my buddy sold his TTR600 long before I bought the TT600RE. Hard to compare unless ridden back to back.
Yamaha XT600E '01, Honda XR400 '03, Yamaha XT550 '83