Wish I'd done better research instead of relying on faulty intuition. In case anyone else has this question downwind...
The Whale Gusher galley
pump always seemed like it had a lot of pressure but according to Whale it has a discharge head of 10 feet - which converts to about 4.5psi. The Sea Gull filter requires a minimum of 30psi.
The Shur-Flo main water
pump is 45psi. The Grohe galley faucet cold water comes off the Tee immediately down from the pump so I inserted the Sea Gull inline there. All cold water at the galley is filtered which is a downside but there's plenty of pressure to get through the filter. The filter is rated for 1000 gallon.