villain is 51/8/2.5 over 35 hands. is this an easy call, or do i put him AI?

Ultimate Bet No-Limit Hold'em, $.25 BB (4 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

UTG ($25)
Button ($14.23)
SB ($30.90)
Hero ($54.42)

Preflop: Hero is BB with A, 2.
2 folds, SB completes, Hero checks.

Flop: ($0.50) Q, 6, 4 (2 players)
SB checks, Hero bets $0.5, SB calls $0.50.

Turn: ($1.50) 8 (2 players)
SB checks, Hero bets $1, SB calls $1.

River: ($3.50) 6 (2 players)
SB checks, Hero bets $4.25, SB raises to $8.5, Hero ???