The interface of the SD7 looks very clean and organised with nice large icons to push..but as you indicate, there are some buttons missing, where the pa3x has all the buttons readilly available but certain things on the touchscreen get to small..

Worst touchscreen interface is currently the Kronos, where many things just are way to small and you need a stylus to work comfortable with them..

Another good touchscreen interface is the Yamaha clavinova CVP line. Its big and works like a charm. But when playing with it, one starts to miss the buttons one is used from his arrangers. Sure there are a few freely programmable buttons, yet thats not enough

King of the mountain in my opinion is the new Wersi OAX, which works like a dream, but then it comes on an Organ of €17000 and its 13" you would not expect anything less, but it indeed is a huge step up from the OAS system..