You should be getting way more than 4500 RPMs. My engine is extremely strong and I'm always concerned with over reving. I like to keep it below 5200, but depending on which prop and condition of the prop I touch 5400 at WOT. With the ACME 431, I'm pretty sure I touching at least 50mph, likely 52ish.
I've had this boat since 98 and have lots of lessons learned. Another upgrade was replacing the standard ignition with breakerless. I actually bought the whole distributor assembly. ($173 at the time from dim) Quite easy, just pull the old distributor out, drop in the new one, and time it.
I had a winterization brain cramp two years ago that caused a cracked block. After opening the petcock, I didn't poke it with a hanger. Sand in the petcock caused water to stay in it. I created a temporary closed cooling system to run Moroso Ceramic Seal through the block. It sealed the crack and I ran an entire summer on the motor. I was just fearful it would let loose at a bad moment. Last winter I had the motor rebuilt with a new block. Since I had the motor out I also replaced the carpet. The new motor runs great, but I now have a slight leak at the rear main seal. Not a major repair in terms of part cost, but I do need to pull the motor out this winter to replace the seal.
Are you getting a nice blue puff of smoke when you start it after the engine has been running? The valve stem guides on the heads aren't nurled down to allow for rubber valve stem seals. I had the valve stem guides cut down on the heads to allow clearance for the rubber seals when I had the new block built. No more blue puff. It's not worth doing if your not having any other work done.