Thank you all for replying.
The question stems from us thinking about buying a one off light water ballasted boat that was never designed to any rule. Its rating under IRC and ORCi is very high for anything except downwind in breeze. (ie it has never sailed to its rating except for downwind ocean racing.)
So the boat will not compete with irc designed boats which is fine.
Could the ORCi rating and vpps be used as a rough guide to the boats potential or are they often wrong due to programming glitches.
An example is at 120 degrees in 20 knots it should be doing 16.6 kn which is pretty fast for a small keel boat. This would seem optimistic to me and faster than most boats.
It appears that ORCi is tough on water ballast and canting keels.
IMHO (unashamedly as another "knucklehead online"), I think your decision on buying this boat should not be driven by relative merits of rating rules, accuracy of VPP's etc. Comes down to what you are seeking from your sailing: if your focus is to go fast around the track and generally have a blast on the water beating larger boats over the line, with perhaps with a casual interest on results based on performance handicap, then this may be boat for you - but don't complain in the bar later about how it doesn't rate on a measurement rating system!. If your focus is to have a decent chance of winning races on a measurement rating basis, then whether its IRC, ORCi or any other measurement rating system, you probably should look at another type of boat. This is from some experience... over the years I have gone from owning/sailing on boats with an IOR-focus to a go-fast, performance-based boat during the IOR ->IMS days, and more recently back into boats with an IRC focus. Had fun on them all.