So is it safe to say that a synthetic 10W40 will provide as much or more cushion as a dino 20W50 and flow better? This is kinda the thought I had in my selection of Amsoil synthetic 10W40.

I agree totally about having the proper film coating to prevent metal to metal wear. The reason I like Mobil-1 20W-50 is that it is truly a straight weight 50 PAO. It has absolutely zero polymers added. It has the "pumpability" of a 20 WT oil and you therefore do not have the resistance you get with a conventional straight 30W or 50W. It is labeled 20W-50 because it has those properties when tested. Nirvana.

As you know every other multi-vis has a thin base and polymers added to beef it up as temps. increase. That's fine; but in hard running engines the polymers become mush quickly. That's why Mercury usus a 25W-40W straight weight conventional blend. It shears a lot less than most 20W-50 conventionals. They know what they are doing; it's just that V-Twin and 20W-60 Redline which is also a "straight weight" 50-60ish oil with pumpability at 20W is great, Your engine thinks it is a 20W but it really it is a 50W.

I talked to a Petro-chemist and he agreed that the V-Twin and Redline products mentioned above are superior products and most likely a derivative of related products and reformulated additives from a Turbine Jet Lubricant Formulation. It will run bearings 20% cooler. In a heavilly modified engine you want this stuff!

15W-50 Redcap is fine for most everyone else unless you want added insurance; like any insurance policy if you have it you are less likely to need it.

It depends.
If you know the engine has been well maintained, as far as regular oil changes, you shouldn't have trouble. My engine has over 400 hours on it when I bought the boat and first thing I did was switch to Mobil 1. After four years I have no problems so far.
One thing to watch out for is oil leaks. Synthetic oil acts like a solvent and will flush any hardened deposits left behind by the mineral oil. These deposits will seal small leaks, like valve covers. After running synthetic these small leaks could/will open up. This is why some people that switch to synthetics in engines with high mileage complain about bad oil leaks.
My old truck had that happen. I switched to Mobil 1 at 50K miles and about a month later I had oil running out the valve cover gaskets. I had replaced them about three months before running Mobil 1. I pulled the covers and used Permatex Ultra Copper RTV in place of conventional gaskets.
What I found under the covers confirmed my thoughts. Every place the synthetic oil had continuously splashed was perfectly clean. Like new steel. The engine castings looked like new. All the other areas still had a varnish coating left by the mineral oil. Be prepaired, it could happen to you.

Has anyone actually experienced a performance gain by using Amsoil over Mobil 1?

Have never used Mobil 1. Only AMSOIL. Why do you ask these questions about AMSOIL? Did you have a problem with it? I noticed an earlier post from you too.

I use Royal Purple 20/50 but I also have a pre-oiler which provides me with 20psi oil pressure before starting.Gives me that "warm fuzzy" feeling that no matter how long my boat sits up,everything is oiled before starting.

I've head a lot of positive things about Amsoil. Never used. Only used Mobil 1.

I put amsoil in my truck and picked up around 1-2mpg. Runs smoother too....... 9000 miles between oil changes. That alone pays for itself.

I use Amsoil in everything I own, boat, truck, car, tractor, mower. Who is Blaster anyway a Castrol Salesman?

I can't even imagine any oil (of the same viscosity) could ever produce a noticeable hp increase, gas mileage increase, or seem "smoother" than another.

Any perceived immediate gain seems more like a placebo effect to me.
-just my 2cents.