Spoke with local friendly tyre shop and he showed the difference between RFT and non RFT same brand of tyres [PS3]. Sidewall stiffness completely different. He likened the "RFT v non-RFT" mix and match to the "cross ply v radial" debate ~ 40yrs ago !!!
He would sooner sell me 2 more RFT for same monet as non RFT [like I said he's a friend] than put non RFT on one axle with existing RFT on the other.
Thats my 1p's worth....