Ya i also read somewhere that when you are doing a build, you have to match your cam to your impellor?

As a rule of thumb, you should always decrease your impeller trim one size, i.e. "A" to "B" when going to a hotter cam.  The jet drive needs lots of torque on the top end a very little below 3000 RPM so you must carefully match your new torque curve/HP curve to the impeller SHP absorption curve.  If you also add cubic inches then an impeller size change may not be needed.

That statement is a little reversed....I am no pump expert but heres a quote from the link below:

based on your info given, you might want to change to a $tainle$$ impeller.

also, heres some more good info on imepller to engine matching:

http://www.cpperformance.com/TechTips/impeller.htm

I'm interested in hearing what opinions, if any, that may be out there for impeller selection.

The boat.........

21 Ultra 21 XS - a relatively heavy boat by design.  Add in several batteries, large sound system and you're up to damn near 4,500 lbs

The motor........

523 cu
700 hp at 6500 rpm
670 ft lbs at 5200 rpm
on the DTS Dyno

The pump......

Berk 12 JG
Mag-bronze legend a/b
inducer
set back

Any pump gurus wanna give it a shot?

Thanks in advance

ROC

first...a mag/bronze impeller is fine in your application. i've put over 1000hp to mag bronze impellers with zero problems. You dont need a stainless impeller. (no offense brad)

your motor makes peak power at a fairly high rpm level. peak hp is what you want to worry about when sizing the impeller to the engine.

how many rpm does the engine turn at wide open throttle when driving through in smooth water?

is this Wes' old boat?