pump sizes

Hi all, I'm new to saltwater fish keeping but I have many years experience with FW. I'm ordering a 10ft by 2ft by 2ft (400 gal / 1500 L with sump) custom tank complete with a large sump, overflow, auto top-off etc. Fully plumbed. I'm planning on making it a FO (mainly larger angels, wrasse...

Okay I can probably get a good deal on a 75 gallon sump and an "ocean runner or6500" 1625gph pump... I'm planning on getting a bigger tank and was wondering if this pump and sump is too big for a 75gal or a 90gal display... I've got a 55 gallon tank and never had a sump so I'm new to that...