2 Fours, Part 2

I posed the following scenario yesterday. Well, the river card and villain's bet puts me to another decision...

Full Tilt Poker, $0.25/$0.50 NL Hold'em Cash Game, 6 Players
LeggoPoker.com - Hand History Converter

CO: $50.20
BTN: $56
Hero (SB): $90.75
BB: $50.75
UTG: $74.10
MP: $80.50

Pre-Flop: 4 4 dealt to Hero (SB)
UTG folds,
MP raises to $1.75,
CO folds,
BTN calls $1.75,
Hero calls $1.50,
BB folds

Flop: ($5.75) 6 7 5 (3 Players)
Hero checks,
MP bets $4,
BTN folds,
Hero calls $4
Turn: ($13.75) 8 (2 Players)
Hero checks,
MP bets $6,
Hero calls $6

I decided to call here. I like the straight of course, but I don't have the confidence here to risk making this a giant pot.

River: ($25.75) 6 (2 Players)
Hero checks, MP bets $26, Hero?