I haven't used Peco track, but my last layout was 100% Micro-Engineering flex track. It is possible to get a nice, smooth curve in the track, but it takes some work. Unlike Atlas flex track that just springs into a curve by flexing it, you have to start at one end of the piece of flex track and work a little bit of curve into it the entire length, then repeat into a tighter radius multiple times until you reach the desired radius. Laying out the desired radius with a Sharpie marker helps, as does getting your eyes down close to the rails and sighting down the line to make sure the curve is smooth and kink free.
The attached photo shows 3 identical curves done with Micro-Engineering track. A little practice, some good luck and a lot of patience will get you your desired results.
Regards,
Don Z.