I think I caught a Mite Invader in the wild!
Win7, Intel i7-2630QM CPU @ 2.00 GHZ(8 CPUs), 6k memory.
Two graphics ‘cards’, one integrated and crummy and the other still-integrated-but-slightly-less-crummy.
The beta operates just fine with no noticeable slowdowns or pauses, and has been what I’ve been using since I picked the game up.
But I noticed it’s significantly behind the mainline version, so I switched back to that - and got the aforementioned slowdowns.
Currently running borderless fullscreen; I’ll try switching which ‘card’ I’m using and let you know if that affects anything.
All drivers are updated to the latest; this could still very well be a hardware problem, but just in case, uh, now you know.
And knowing’s half the battle!..