The point about stiffness is that it could be different in many places over the racket. The biggest problem I guess it is to get flexible frame with good feedback. Some Prince frames with O ports were really flexible and powerful – but the feedback was awfull. You can't have control with such frame.
Some older Dunlop frames had both nice flex along feedback – but some people missed power (I really love Bio200 and some others). With 231 you have tons of power and flexible frame – but feedback isn't as good as from PT57A or let's say classic Prestige Mid frames.
I would even say that I prefer retail Liquidmetal Radical MP over 231 for feedback/touch.
Also with prostock frame – it is up to you how much weight you want. In my opinion PT57A plays better around Pro Tour 630 specs – which is a bit too much weight for me most recently. Once PT57A is getting less and less heavy – it is still stable, flexy and has great feedback, but
the power is gone. Then it is easier to pick up 231 – more power at similar weight.
It really depends on what you expect from the racket. I love feedback and flex of PT57A – but I simply play better with a bit stiffer hoop and lower weight. I like to play with iPrestige, Microgel/IG Prestiges or some old Dunlops (but they do need great footwork as all power comes from your mechanics!) – but the comfort and power is worse than PT57A.
I found two retail rackets to flex similar to PT57A – Wilson Blade 98 v7 and Yonex Ezone. While I couldn't play with Yonex – I am still trying to get into Blade 98v7 for its lower weight, bigger headsize (and sweetspot), nice stability, comfort and acceptable feedback.
