So after much thought ,I have decided to go with the original plans- which are V bearings and Rack and pinion.
This is purely a cost thing for me - the entire build should come in at under £2k. I can understand peoples views on linear rails and ball screws but as pointed out by some ,it would take the build cost to nearer £4k which I am not prepared to spend.
Also the fact that this is an 8 x 4 machine for that price I can't see me having any 'Regrets' building it! like I have said before I would rather have a cheaper machine running than no machine at all.
If there is some upkeep to maintain performance then so be it.
Speaking to one of the guys who have built this he said he would build it again in a heartbeat.... but no need as its still running 7 years later ,now upgraded to aluminium carriages but still running V rails.
So bearings are ordered and aluminium profiles and angle iron are in this week :)