JM,
Regarding the notched transom, I have been nearshore out of Manesquan Inlet. No water issues. Coming back though through the inlet, I did find myself watching the rolls behind me, and really dialing in between the waves. If I had the closed transom I might worry less about that, but might not be developing my skills as much. SO it is a double edged sword.
I didn't test drive the 2520XL 16 degree deadrise at the dealer; but my friend has it. I would rather have it than my SL. But it all comes down to coin doesn't it alway?
I found my boat slighlty used, through word of mouth, and my several month old boat, with the Yamaha F250, was a probably $20k cheaper than the XL. Truth be told my boat is fine for what I do and where I go, and the kind of weather I go in. It really is. I have also heard it said that it is easier to back into a slip with (without the bracket), and that my slip cost would be cheaper because the LOA is less.
It is very easy to really get into the minutia comparing so many boats: Parker 2520SL vs 2520XL vs 2520MV vs 2520DV vs Steiger 25 vs....
The fact remains that they are all good boats, and none of them are designed to run like a deepV Grady or Contender offshore, and their rides will likley be a derivative of 85% Captain skill/ 15% deadrise. Or something like that!
If you have the money though, you really should test drive a 2520XL with twin 150's or twin 200's. Something tells me the weight distribution on that boats would make for a sweet ride. Many complain about how forward the helm is on the Parkers, and I think the weight of twins and a bracket is at least something you should check out. If you have the coin.