Re water jets for model ships:- A couple of years ago I read an article in 'Popular Mechanics' (South African edition) about a chap who built quite a large model of one of the SA Navy's new Meko A200 frigates, the SAS Amatola. As well as having two conventional screws, they also have a single, gas turbine powered water-jet for the occasional 'sprint' - quite impressive to see! Anyway, on his model he used a fish tank water pump to simulate the jet on the full-size vessel. Unfortunately it didn't state what size or how fast it powered the model, but perhaps this is worth looking into as an alternative to the units mentioned in your query? Just a thought!
Regards,
Glyn