I used my RT51 with single side Time Atac they are quite stiff – used reg on a 60mile round trip commute..
nice to be able to walk up and down the perilous stairs to the basement without a road cleat sticking out..
also used them for Lejog on my brompton – 110miles a day – never had a hot spot. I do have Specialized wedges and footbeds in them.
you will often get more position issues on a road bike than your MTB as your position is much more static on the road.
The Shimano RT shoes are meant to be used with the matching touring single sided pedals as the outer part on these matches up with the shoe sole to give more support – also works with single sided time atac pedals..
if you were happy with two bolt spd, just get some more spd shoes (perhaps stiffer touring or mtb ones) and carry on.