This level of power has been around for years in the aftermarket, is there much of a difference?

Here we go....huge difference...

four words : no more push rods

you can rev them safely and still make power...

Reliability, aluminum blocks/heads, Quad Overhead Cam Heads...liner problems and the rest of the issues that always come along with the 1st generation of motors.

See how long a true 1650hp motor will stay together in a race application, sure 6-8 seconds you can make them last. Sure it's been around for years, but making it live for more than 2 laps, or 25 minutes is a feat. Merc has managed to get over that hurtle but still has some bumpy ground to make up. That's what happens when you do all this new tech at once.

My .02 cents.

It's not how fast you run it's how long you run fast that matters. These motors run fast a long time.

reliability and the mercury brand

IMO- I think over rated for the price. I think the real ticket in the push rod engines is the E type fuel!! E85, E98, E108, E114... If you don't know, you should google it!! Huge difference!!! Or just check out Ignite Racing Fuels site!!! Hey the new Mercs are great, but just not for me!! Plus you have to get the power to the water, and the M8 Drive can not compete with a 6!!! AND I've already heard my share of blown up 1350s and broken M8 drives. It's gonna still happen!!

Valve train stability is the problem, fuel won't fix that16 big valves vs 32 smaller ones. plus turbo charging, makes for all sorts of torque management and power delivery options. What is E108 and E114?. The "E" is percentage of ethanol not an octane number. E100 is the max but that would be drinkable and subject to alcohol tax and laws etc. 2% gasoline is added to denture (poison) it., E98. M8 is that same design as #6 just beefed up, if they are breaking M8's then a #6 would break too.

The biggest problem I see with the Merc 1350s and 1650s is they're not in my boat!

Look it up, and the 8 is NOT the same design!! And I'm not talking about breaking them. I'm talking about performance and hydrodynamic drag!!

Here you go
http://www.igniteracingfuel.com/

Sound's a lot like when Mercury Racing developed the VSSM and bought the K drive (renamed VISSM) The 5 is faster! The 6 is stronger! And here we are decades later, at the crossroads again.