Scroll your game somewhere where there is nothing visible on screen at all (maybe make some custom events to do this). If the game speeds up, it's rendering. If it doesn't, it's events.
well, game runs at around 15fps when scrolled outside view, so I believe it's in events, but are you sure that offscreen drawing doesnt affect speed? is there really a difference if the sprites are drawn on or off screen?
cheers and thanks for the help