Has the CPU monitor window in Logic Pro X changed to now be called Performance Meter and reads at the bottom Processing Threads and Drive I/O

Yes, the latest version of Logic lists the CPU/HD meter as Performance Meter and comes in two sizes now.

Note: in the Transport (control bar) Setup it's Listed as 'Performance Meter (CPU/HD)".

To get the large size hold down the option key while selecting the PM.

Small

Large