7 suspects

Bob kirkland - As the promo for Red Listed tells us,he probably isnt RJ and is just a big red herring.
Reede Smith - Viewers may feel cheated if it was him since he has only been shown for a few minutes ever
Brett patridge - Dead (unless Heller is messing with us)
Bret Stiles - Too old and his previous episodes or RJ descriptions would not make sense
Sheriff McAllister- Has been in 1 episode before season 6 and made no lasting impression on viewers
 
Leaving 2 solid suspects that would be satisfactory.

Gale Bertram - Fits the mental characteristics but not physical.However we cannot judge on Rosalinds description
Ray Haffner - Seems to fit all parts of RJ description but is an obvious choice

This being said, I know for a fact that Heller will be able to leave us all mindblown by the revalation of who is RJ and is not going to pick one of these men and just say 'Hey, I'm Red John'. There will be a lot of twists and turns until we reach episode 8.