I LOVE that you got to 65,000!
So that is the result of the maximum value of an unsigned short, which is to say two bytes, on the 16bit register.
What I did to get around this value limit of 65,535 - was to find an example of a software defined 32bit register.
I don't know that I got it correct though - but the early version is up now!
Also let me know if you see a slight improvement in gameplay speed after level 7. I don't think I nailed the screen frame budget bug - but I think i might be on the right path.
THANKS FOR PLAYING!