Can't comment on the 8.3 particularly although I have seen it at a few stages of it's development and birth but can certainly comment on the 6.3 that I own (the very first!).
Firstly, you need to understand that you will open a whole can of worms regarding where the design came from and that you will get grief and comment on here about that. If you can see past that then I will make the following observations:
Build quality - superb, two years of hard use (100+ hours/annum in all weather as it gets commuted on for yacht racing as well as the "family stuff") and there is little sign of wear and tear.
Ride - generally very good. It is trim sensitive and rides much better higher up. Despite appearing low nosed ('cos of tapered tubes) it's rare to feel threatened by waves up or downwind unless it's seriously breezy and short and sharp chop (in which case you simply "tack" downwind).
Rigging - mine left a little to be desired as the proto boat and I have spent time changing things a bit to make them more user-friendly and acceptable. I would ask the questions first as to whether later boats have improved (or simply manage the process yourself). Silly things like tube fittings and the like should have been improved although the integrity of the tubes themselves is very good.
Economy/performance - exceptional, maybe because of it's "heritage". Mine runs an Evinrude DI115 and over 2 years has seen an average fuel use of 10l/hour in mixed use (some WOT, some skiing/wakeboarding etc). It planes early (lower than the 10kn speed limit in Portsmouth Harbour, with some weight in the nose) and efficiently. These figures have been checked with owners of boat no. 3 (a 115 Optimax) and 4 (a 90 Mariner) and found to be similar! With a 19 pitch prop it sees 45kn at WOT and cruises comfortably at 30kn (4k revs) with 4 people. It also has sufficient punch to get me (98kg) out on a wakeboard with no problems (although trim in and weight forward helps when there are 5 others on the boat!).
Generally I am pleased with mine, although I would look seriously at the rigging. I am looking to go bigger and will be talking to Lee, which has got to be a good sign.....................
Cue the abuse from Jonny F and others