I'd say the mutation options are Big Hand, Claw (not worth it unless you have might blow first) and Very Long Legs (which is also not so hot when you have an AG5 player, but it still has some use.)
The AG5 Gutter Runner is going to be doing 90% of the neat ball recovery tricks by himself, this leaves room for the doubles Gutter Runner to develop in a different manner.
The very best (non-stat increased) LRB5 gutter runners I've seen are:
Block, VLL, Big Hand, Leap
Block, Strip Ball, VLL, Leap
Block, Mighty Blow, Tackle, Dauntless, Claw (That's the exact order he gained the skills in)
Catch, VLL, Pass Block
The first two worked in tandem on the same team to set up turnovers of ball possesion - and pretty much forced Sure Hands onto every team in the league. The third one ended up second place in total casualties for the league (behind my Block, Claw, MB, Piling On Nurgle Warrior.) His owner always said if he got to that final skill he would take Piling On if he got a third doubles.
