I have the XL which is a little heavier than the SL and we stepped up from a 1991 2520 mod v with the 14 degree DR.
The XL rides good, but I know there are days the DV would help us through the chop better. We bought the boat used and there are not many DV XL's around so we could not really be to picky.
If we were looking at 2 similar boats such as the case you are in I would go DV. In addition, I am assuming the DV you are looking at has been used during the past season-the other boat was not winterized and not used in 16 months. thats a lot of time for the engine to be sitting around and for the boat gremlins to got to work sabotaging it.
Parker hulls are great-our 91 was solid-so the year of the boat does not really matter unless there is a specific design change you would prefer. However, the engines over the years do improve. Personally, I would prefer a newer engine then a newer hull.
In addition, if you want your engine data to show up on those new electronics you are buying you need the 2006 yamaha. We were hoping to get engine data to show up on our new Simrad NSS but found out Yamaha did not implement that until the 2006 model year.