Firstly I should point out that the background scrolling stuff in my sprite demo is really inefficient & is only there to support the sprites which in themselves are as fast as PF could make them without dropping classes for inline code. While I have a J710 I have not tried to improve the frame rate on my code however the existing PF demos run quite well though of course slower than PocketPC.
Re: coding on the device I have used PocketC in the past but it's not really a 'C' and recently I've tried various text editors to find a good code editor without success but having access to a new/small/light XP prof laptop makes it silly to try to code on the J710 but I still love the HPC format & won't part with my device.