Im quite a SIB fan myself, and i would definately reccomend the wooden floor. Aside from the wooden floor being more rigid, it gives you a base for securing items such as fuel tanks, and adding foot straps ect, which i have done with a SIB in the past, also using a slightly thicker floor board.
I'm not sure on the lighter boat nessacarily being the better boat, rather that the weight would effect it's preformance given certain conditions.
I currently have the Zodiac 2.85 fastroller, (funnily enough with a 30 Tohatsu) which is the version with a wooden floor and an inflatable keel. I have been in the 2.7 air deck, and i much prefer the hard floor. I know they are both 1m shy or more of the ones you are looking at, but based on the performance of their smaller siblings, should give a good indication of thier performance.
The 380 HD is without doubt a fantastic boat, and has been tried, tested, and proven itself amongst a host of other SIB offerings.
Good luck with your decision, by my vote definately goes to the 38HD. Go with what you allready know is good, and your guaranteed to be happy !!!