Still collating information from everyone, but it's been really helpful so far!
Advice from most people so far is to up upgrade the LCR rear to 28mm as this decreases most of the body roll (plus a Neuspeed rear ARB is adjustable so can be tweaked too). I've been taking great interest in watching cars corner at speed lately and notice in most cases it is the rear that lifts the most.
Over-stiffening the front might also not be a good idea as I know it isn't optimal to stiffen up the drive axel too much - as on cornering or bumpy roads you can actually lose traction, which obviously isn't a good thing. When I was researching I noticed almost all ARB kits for RWD cars have a smaller bar at the rear for this reason.
On the other hand I don't want a skittish car, with the rear jumping about from an overly stiff rear-end, but all comments so far seem to point to the fact that the LCR is quite an understeery car to begin with and it wouldn't
help the cars handling if the front end was stiffend up too much (and since having the GY Asymmetrics fitted on my car - better tyres on rear - has removed any lift-off oversteer anyway).
I am now pretty much swayed towards a 28mm adjustable Neuspeed rear ARB and a smaller front ARB. An upgrade of the front ARB is definately required though as the OEM 18mm bar would be much too small in this combination and the balance wouldn't be right as discussed in the autocross thread that started the debate.
I think it will either be 22mm Neuspeed, 23mm R32, or 25mm Neuspeed, but I would now actually be a little worried that 25mm would be too stiff at the front. I want the right balance front to rear but don't want a skittish rear end and don't want an overly stiff front end that will lose traction accelerating out of slower corners.
Dean at Awesome GTI recommended 22/28 Neuspeed - obviously he sells these, but he did recommend 22 over 25 for the front. Willie recommends 23/28 and has tracked his car a few times with. The autocross thread recommend keeping the bars relatively in sync and found handling issues with the 17/28 setup in a different older VAG car.
Going from 18mm at the front to 22mm, 23mm or 25mm would be an increase of 123%, 167% or 272% respectively, so a 25mm bar would be a MASSIVE increase in stiffness of close to 4x original and so I think the other two bars might be a better option...
Still up in the air, but I think it might be 22 or 23 front and 28mm rear. Anyone who hasn't commented yet, by the way - please feel free to do so!