To CB or not to CB

[castigar]

Should I still CB on big pots like this w/out reads? Sometimes I make the guy fold but when I don't, it costs me quite a bunch... What do you do?

Full Tilt Poker - No Limit Hold'em Cash Game - $0.10/$0.25 Blinds - 6 Players - (LegoPoker HH Converter)

Hero (SB): $35.85
BB: $34.75
UTG: $5.70
MP: $10.40
CO: $25.55
BTN: $18.25

Preflop: Hero is dealt A[img]/images/graemlins/club.gif[/img] K[img]/images/graemlins/club.gif[/img] (6 Players)
UTG calls $0.25, MP calls $0.25, <font color="red">CO raises to $1.25</font>, BTN folds, <font color="red">Hero raises to $4.00</font>, 3 folds, CO calls $2.75

Flop: ($8.75) 4[img]/images/graemlins/spade.gif[/img] 5[img]/images/graemlins/diamond.gif[/img] 4[img]/images/graemlins/diamond.gif[/img] (2 Players)
<font color="red">Hero bets $6.00</font>, <font color="red">CO raises to $15.00</font>, Hero folds
Uncalled bet of $9.00 returned to CO

Pot Size: $20.75 ($1 Rake)