I currently have a frame using a BB30 BB with a Race Face turbine crank. As far as I know this means it has a 30mm spindle.

I’m considering swapping frames, and the new frame has a screw fit bb. Does this require a different spindle size, and as such a new crankset?

Need a 30mm screw in Bb like this one from hope
http://www.hopetech.com/product/bottom-bracket-30mm-threaded/

Hmmmm, financially better off selling existing cranks and getting a new/used set.

But you’ll need a new bottom bracket regardless of what cranks you run when you change frame. Why not just get one that works with your existing cranks? Especially as they’re good cranks.