Finally found the right place to post this!
Looking for a 2S Lipo recommendation.. Was debating between the Orion 4500, 100c shorty, and the reedy 70c
I will be using it in a t5m running in the mod class, 8.5 motor.
Back after a 15 year layoff-- trying to read and learn as fast as possible.
Thanks in advance.

Flip a coin - either one of those will be more than enough battery for your application. In modern mod racing, the cars make so much power from the motor and run so efficiently in terms of run time that many mod racers will actually chose a lower/cheaper spec'd battery to deliberately get a higher ir that smooths power delivery.

I've used both Orion and reedy lipos. Both get the job done.