So, an update - I fiddled with the cleat positions on my Campagnolo Pro-Fit pedals again at the weekend, I moved them both back a little bit (though there would still be scope for moving them back further) and moved the left one in board slightly, so the crank no longer rubs on the toe covers.
I then did a quite relaxed 30 mile "social" ride with my local cycling club on Sunday, wearing quite thick woollen socks and tried not to over-tighten the boas. I also tried consciously to avoid clawing the soles with my feet and to try to keep them more relaxed.
Results were quite promising, no foot pain from the sole and the ends of my feet didn't go numb at all (bearing in mind it was quite chilly) though obviously this was quite a short ride, there were no serious hills nor was I ever really pushing that hard on the flat, so more testing will be required.
When I look at the cleat positions, it *looks* like I have them setup in exactly the same position on both shoes, though the position still doesn't *feel* quite right on the left - guess my feet must be different!
Also when I bring my ankles in as close to the cranks as the float will allow, the shoes are pointing dead forward, though my feet feel like they would like to be able to rotate slightly "duck-footed" I.e. a a bit more movement of the ankle towards the crank - I don't usually walk duck footed at all, as far as I'm aware, but it feels slightly odd to be constrained from moving at all in that direction off-centre. Should I rotate the cleats slightly to try to allow a little float inwards, or is that bad practice?