JK I suppose everything with a deadrise of more that 23Deg is a modified Deep V.
To try and describe it is to say where the expected planing surface starts e.g aprox 2/3rds down the hull at the bottom of the Deadrise there is the start of a flat section that extends aft to the transom cutting the V into small A withought the top bit.This A/Flat piece could be aprox 6/18 inches off the bottom of the V when it arrives at the Transom and the length/height is down to different builders experience.
The concept is that providing more lift withought compromising the deep V at the criticle point it goes faster for less power and when deep V is needed it is there when it is required.
Its a balanceing act.
To achieve a efficient Delta Keel you need to do lots of testing,this can be done within a reasonable budget and the size of the delta/flat can be experimented with to find the best size/ height/length to achieve the optimum performance for the given hull length and weight.
I havnt seen the XR but I suppose even if I had I cant comment on there design as some people will get it right and some will get it wrong.
With a fibrglass hull mould this sort of experimentation can be very expensive and usualy you try and get a good all rounder first off when the hull mould is built.
Its interesting as the stepped hull concept came from the US and ended in court action in the UK I beleive.
The length width height of our Delta keel is a closely guarded secret by our builders as the cost of developments were high and the info gleaned is commercialy sensative.
The Acid test is what otheres think who know of the builders designs and there ribs, and one takes into account there established reputation within there respective market place for producing offshore ribs.
If they are respected for there achievments and quality then you give it a shot.