On most of the Q family the SFR registers are in banks 0-4, and the start of user ram is in bank 5.
That's where the access bank is (0x500-0x55F). The other part of the access bank is at 0x460-0x4FF, but that's for the fast SFR registers so you can't use that.
So, the "default" setting for 'banksel' should be 5 and not 0.

If you use the MOVFF instruction both the source and destination must be in the first 4K of ram space.
If either are outside that you need to use MOVFFL, which is a three-word instruction so it's more code (and slower) than MOVFF.

The K42/K83 force you to use MOVFFL to access SFR registers outside the access bank since on those the SFR regs are at the very top of ram.
That's one reason to skip the K42 and use the Q43 instead.