I've used Speedplays (stainless Xs) on road bikes but as mentioned, the cleats are tricky to walk on even with covers.
I've now swopped to Crank Brothers' Candy (mtb) and Quattros (road) now - they have similarly large float but the cleats are recessed like spds. I find the ease of use (four sided, so there's never any issue with flicking the pedal into the right orientation), large float and ability to walk in them is an ideal combination. Also, I'm a 'bent rider and you need good grip on the 'down' foot when you stop as your weight isn't over it in the same way as when you put a foot down on an upright. Like Speedplays, there's a choice of chromoly, stainless and Ti, depending on your budget.