To be honest, the more the merrier (to a point). Most fish that go into a fowlr are just as capable swimmers, if not more so, then most 'reef fish.' Unless you are going for specifc fish that aren't the best swimmers, puffers, lionship, frogfish, etc, I really don't see a reason to have lower flow rates. It's just like a reef tank, strong water movement is good, but a bunch of jets blasting everything isn't really good.
And not to pry into your personal stuff, but everytime I hear "fowlr and a tank under 70gals or so" I cringe a bit. Hopefully you are planning on an appropriate stocklist for that sized tank? Or if you're doing like some species frogfish tank or something, I should have shut my pie hole long ago..