You have 33% pot equity on the flop against an overpair and a made straight, justifying a call if you can get the CO to call too, perhaps getting him to pushing over the top and give you a decent side pot to win.
http://twodimes.net/h/?z=1298696
pokenum -h 4s 4d - 6h 5h - as ad -- 8s 7c 4h
Holdem Hi: 903 enumerated boards containing 8s 7c 4h
cards win %win lose %lose tie %tie EV
4s 4d 301 33.33 593 65.67 9 1.00 0.337
6h 5h 574 63.57 320 35.44 9 1.00 0.639
As Ad 19 2.10 875 96.90 9 1.00 0.024
Pushing all-in is bad because it only picks up ~1% of pot equity for you:
http://twodimes.net/h/?z=1298704
pokenum -h 4s 4d - 6h 5h -- 8s 7c 4h
Holdem Hi: 990 enumerated boards containing 8s 7c 4h
cards win %win lose %lose tie %tie EV
4s 4d 339 34.24 642 64.85 9 0.91 0.347
6h 5h 642 64.85 339 34.24 9 0.91 0.653
The bad times are when CO or BB has a higher set.
Since you don't have any reads, I think a fold is the best choice since I can't imagine CO folding here.