bigfred 

Unless the OP has found something I'm unaware of, the only Shimano shoes available in 51 and 52 are the mid-range 80 Series road and mtb models, which have plastic soles.

I have a pair of R86's and can confirm that they aren't particularly stiff compared to my ancient pair of Sidi Genius. Even though the Sidi's are also a plastic sole.

It sounds like the current Genius 5's have "some" carbon content in their otherwise injection molded sole, so might be stiffer still.

I don't see why you couldn't try drilling your own holes for the direct mounting. I know that speed plays are sensitive to warp issues and you might have to pay a little special attention. But, it should be doable.

From speedplay's site:

[h=3]2013 Manufacturers of Shoes that feature the Speedplay-Approved 4-Hole Cleat Mounting Standard:[/h][TABLE]
[TR]
[TD]DMT [/TD]
[TD]Gaerne[/TD]
[/TR]
[TR]
[TD]Lake[/TD]
[TD]Northwave* [/TD]
[/TR]
[TR]
[TD]Rocket 7 [/TD]
[TD]Sidi[/TD]
[/TR]
[/TABLE]


Of these, Sidi appears to only do the Speed Play approved soles in the Genius 6.6 and the Wire. Neither of which come in a 51/52. Neither Lake nor Northwave advertise anything beyond 50.

One thing to keep in mind, is that while reducing pedal stack height may allow you to lower your saddle and subsequently increase the effective stack height of your frame, with feet the size of ours, your cornering clearance is probably already limited by the outside edge of your shoe sole, not the pedal. Lowering your pedal stack height further reduces your shoe clearance in corners. I know from experience just how much it sucks to ground out with, and break, your little toe in the middle of a corner while on the down stroke. If you're frame can accommodate your fit requirements as is, it may be wiser to stick with a higher pedal stack. Especially if you're using 180mm cranks on an otherwise standard 70mm drop bottom bracket. (sort of assuming the considerable height and inseam come hand in hand with a size 16)