performance upgrades

So im thinking about ordering a performance exhaust as my first upgrade for speed...which one do ya'll recommend? Im new to motorbikes... http://speeddemon.ca/motorized-bicycles/parts/expansion-chamber-muffler-black.html or...

I would like to consider upgrading my head on my Grubee GT-5 and was wondering if anyone has tried either of these heads and what their experience has been? I'm looking for a little extra power and speed, and wondering if it would be worth it over the regular china slant head on the Grubee...