Thanks, I'm really glad to hear that! :)
I just tested your latest version and didn't notice any lag with the first two bosses.
btw. the Groko Bot logo and the screens up to the "Press Start" prompt are slightly off-center, and the resolution seems a bit off during boot. However, as soon as the main menu hits, everything scales and centers perfectly!
I just wanted to make you aware of it. Should I go ahead and use this version anyway?