I'm thinking about a 2002 or a 2004 400SS. One has 500's with 400 hours and the other has 525's with 200 hours. Anything particular to these years that I should on the lookout for?

i have an 06 400ss with 525and almost 200 hrs and have had zero problems
400 hrs on the 500s probably time for top end if not already done

What kind of performance fuel consumption do you see?

Thinking about looking at diesel. Any thoughts on that? If you could do it over again, would you go for the diesel?

I'd vote for diesels since going faster in these boats is not a priority item for me. I've done the go fast thing for years, and I don't get much of a thrill going 60 in the SS line. Cruising at 35 or so is just fine with me, so diesels would work out nicely.

On the other hand, if you want to tickle 60 then go with the 525s.