I too have a pico stick, but usually fly bigger planes.
I dont think you really need to upgrade to a new plane just yet. The standard stick is a bit weak so I wouldnt aerobat it without strengthening. I braced the wings with fishing twine and fly on 8 cells so it can now do limited aeros. I would try that before building an Und NU as it would be quit a step up from the stick.
Tom.