The AK's sights are fine for what you need them for. They arent target sights, but they work.
Forward mounted peeps dont work like a standard peep, and I always found them to be more difficult to shoot with than the issue sights.
If you really want an upgrade, a good, forward mounted red dot on one of the Ultimak rails is the way to go for the AK. You can still use the iron sights through the tube, and the rifle shoulders and shoots very naturally like it does with the iron sights alone. They make Ultimaks for the M1 Carbine too, and I would imagine it too would benefit in the same way. I just never shot a carbine that had one mounted to say for sure.