I've had issues with hot spots in warm weather on longer rides. The last 10-20 miles of my 80-110 mile Saturday rides get rather torturous with painful hot spots on my feet. I'm convinced that could be because the design of the Speedplays. The Keos have a wider platform. The pedals are slightly heavier than the Ti Zero's (190 grams vs. 150 grams) but the cleats are considerably simpler and 20g lighter, so the pedal/cleat combo is within 20 grams of the lightest pair of Speedplays.
Initial observations: lower profile, easier clipping in, harder clipping out, and I miss the more wide ranging float on the Speedplays (I have the 9º float Keo cleats). But that should be plenty of float for me. They do appear to present a considerably wider and more balanced pedaling platform. I need three sets of pedals for three bikes, but I'm starting with one set. I'm keeping the Speedplays for a while, I'll eBay them once I'm convinced this Keo thing will work. My right knee is bad news, that may be a factor, but I don't think I need the big float of the Speedplays. Another factor: in winter those complicated Speedplay cleats are a major pain. If you get snow/mud in them and try to re-clip, God help you. I ride a ton of miles, the simple Keo cleats are cheaper and will probably last longer. Slightly easier to walk in as well.
Another plus: you don't need a pedal wrench, they use a 6mm allen bolt. That's easier.
One last note: Keo Schmeo, this feels and looks like the same Look pedal design from 1988 with a considerably more svelte carbon form factor. By the way, this is the 'hot' 'new' (looks pretty old to me) pedal at my LBS. Never let it be said that Pcad wasn't a sucker for a good sales pitch. Let's hope this helps my sore footsies. I'll let you know if I can get used to the Keos this week.