Using the SHOW flag instead for the TEXT array objects seems to be a little faster but does show some spikes as well (in time_panels).

EDIT: Drawing bitmaps with draw_quad is much faster (as one would expect) but even there you'll find some spikes. No spikes when I don't use draw_ instructions (saved frame_time into an array, wrote that into a file at the end of the application, so it's draw_ related).