I have a new rtr and I have had to upgrade many parts. The shock towers a big difference, they are much lighter. I talked to a guy with the pro and he said that he could'nt bend them if he tryed. The rtr towers are like rubber and the pro veresions are $ 25.00 each.
Another thing that I had to get right away is the pro wing support.
The diffs are the same.
The Pro engine mount is better, it is also a chassis stiffener. and if you are planing on using a starter box you will need to replace the rtr mount anyway (or cut it)
The cv shafts are a little tuffer.
I think that the shocks are the same
The chassis is a little more trick, it is cut out for weight savings

I bought the rtr for $499.00 and have upgraded:
shock mounts$48.00
clutch bell $15.00
wing support $4.50
springs $12.00
ackerman rack bearings $14.00 ( the rtr has bushings)
engine mount $21.00

Thats $114.00 but I did get a $169.00 spektrum radio.

the engine is very good I will run it this year and upgrade next year.

This is my first year racing and the turmoil hangs with all of the cars. I do recomend the shock towers right away.

good luck