I'm going to do a gbak backup/restore on my 100 Gbyte database this
weekend, and was wondering if perhaps I should bump up the page size
from 8 kbyte to 16 kbyte.

What should I look for?

I'm running gstat -a -i right now. Is this the appropriate options to
get the relevant figures?

There are two tables with roughly 200 million records. Perhaps 1-2
tables with about 20 million records. The rest should be in the range of
100 thousand or less records.

Regards,
Kjell