The Excalibur Concept looks interesting. Have you seen full plans for it yet?
I'm not sure that the Redbay Expedition
actually sits much lower than the other 8.4s. For example, the Canopy boats look identical, so I don't think the cabin weight is having a great effect on the waterline. I suspect that the up-curving deck and high roofline makes the bow look lower, it's a very high cabin to "blend" into an 8.6 meter rib. Have a look at these pics, some I took, one from Redbay's website.
This has been a huge production run, they seem to launch one every eight weeks or so since mid 2005. I've spoken to a few owners and they seem very happy with the sea-keeping qualities (but then, they are biased

). I'd suggest taking a drive up and get
a few hours out in one yourself before you part with €90k!
I've had a quick run in one with someone less restrained at the helm than myself - I was hugely impressed. They can be thrown about much like an open rib but smooth out the lumps as you'd expect from the 8m+ hull.