Does the amp rating of the ESC make a difference?
 

If all things equal: batteries, motor, prop. will a higher amp ESC have better performance?

I've ordered a 2000kv motor to run 3S, and I also ordered a 45 amp ESC.

Should I have gone higher with the ESC?

What size motor? What size boat? What prop? Which ESC? .

The old Shockwave 26 RS that is brushed.
Adding a Dynamite 3650 4 Pole Brushless Marine Motor 2000kv, DYNM3900, and ProBoat 45-Amp Brushless ESC, PRB3309.
The ESC is wired for 2S x 2 packs, but I will only run a single 3S.
FunRCboats.com recommended a 1440 plastic octura prop for testing.
Any other suggestions?

A higher amp esc usually has lower internal resistance therefore a higher voltage delivery to the motor. About you 45amp esc with your 2000kv motor on a 3s pack it should work but I would recomend not changing to a motor with a higher kv on 3s. And please don't put on a prop with a bigger diameter and water cool everything especially the esc. You ask should you have order a higher amp esc and I would say absolutely. You should have gone for something higher like 90amps or above.