I've been using tushingham sails for many years now and before they started to make tushy masts, I used powerex masts and they were great. I don't know if the designers have changed their sails to suit different bend curves, but I don't think they would be that different. I think the main problem for you sounds like it is the way you are rigging your sail. The X15, and all the new tushingham cambered sails require a different rigging method. You should go to tushingham.com and have a look at the rigging videos for your sail. When it is set right I think you will be happy with your new sail.
If you want some profesional

advice, then stop in to 2nd wind and have a chat to Jez or Paul. They will be able to sort you out.