I have a 100gal reef and upgraded from an old QuietOne pump to a Little Giant 4-mqqx-sc which was swamping my two one inch overflows, had to hang an overflow box on the back of the tank and divert h20 to my 50gal tank and protein skimmer, if you chose one inch you will have to live with it forever and any pump upgrades you will have to figure out what to do with the extra h20, if you choose larger now it will be more convenient in the future.
Reaper10