Working on repowering my 308 Flatdeck Skater from 700SCIs. Plan was to put slightly used 500Rs on it but it fell thru. So now since I have some time I am looking for some thoughts on both.
Price difference is $40,000 which most likely will be close to what the boat would be worth addtionally when I sell it. Either way they, both new with warranties.

400R V10 Cheaper, 87 Octane fuel, less maintance, less supercharger whine, Lower end not as robust, slower by 8-10 mph (thinking 115-118 for the 400R), cheaper insurance, same weight, lower cost addtional warranties when its time.
500R 89 Octane, more maintance, FASTER, Robust lower, Easier to sell?, Higher Insurance.

I cruise in the 70-90 mph range now and think I should be able to do the same with 2X the fuel economy and lot less maintance. I had a 28' in the past and decided I am just a outboard guy...

I'll go with brand new engine ≈ warranty, if you dont care the top speed

Just my 2 cents

Seems like an application for 500Rs. This is what they are for.

Given that you are moving away from inboards, the increase in headache from 400R to 500R is insignificant compared to the decrease in headache from inboards to outboards.

Can I ask what 308 you have? 700s with what drives?

Not that I am at all in this zip code and maybe it's because I am older but the 400R's to me would be the ticket.
Reasons:

• 8-10 mph slower but how much time % will you really use that.
• Cheaper insurance=More gas money.
• Longer warranty.
• They are 5.7L and only 400HP, that is NOT a very stressed engine, has to have some pretty good longevity.
• Lower not as robust but do they need it at that power level, have they been failing?
• Lower resell is a minus, but if like you said you get a 40K difference on the repower sounds like that may be a wash.

Not that this means anything, but I'm going with the 400V10's on a new 32 DW build.

MDS

You`re going to love the 400s!!

Until you get passed by a 450R, 500R or a V bottom.!

400Rs are very smooth and quiet with strong midrange. Have them on a 32 DW and runs mid 120s with ease.

This one with ASD7'S from this thread I'm thinking.
ASD7 Rik Wimp - Offshoreonly.com

Hey Michael, I've heard great things about the V10 400R, but I think in your situation, you'll be very disappointed if you go with those. The performance difference between your 700/ASD setup and 400Rs will be night and day, leaving you wishing you never did the rerig imo. At least with the 500Rs it will still have somewhat comparable performance to your existing setup, but with the fuel economy, lower maintenance and quietness of the outboards. I was unfortunate to have no choice but to rerig my 30 w/ the old I6 400R Verados back in 2018, and I was so unhappy with the performance after the rerig that I only ran the boat 1 1/2 seasons before sending it down the road.