The pic that you posted up top is my set up. The reasons that I went and did that were basically because I don't trust just having velcro straps to keep me fixed to the pedal, and I loved the locked in feeling that rat trap pedals give you when you're strapped down. It's a sprinter thing. If you're not that heavy/strong, I wouldn't worry about attaching a strap to any pedal. The regular speedplay X series have great retention, and up to 20 degrees of float. I found that my knees really liked the free float, and with that much float, I've never had an accidental release. Your foot just has way to far to move to hit that point unintentionally. That's just my experience though. I have SPD-R's on my road bike and they work really well for me too, but I had the speedplay X's for the longest time prior to them. I would go with the speedplay system over the spd-r just because of personal preference, but they two are really close. I basically went with the speedplays because I had them first.
The track version of the speedplays are just teh Zero pedal with a stiffer release spring in the cleat body. It's cross section is a lot wider than the road going version. 11.4 is right in that the release is more abrupt, but only slightly more. You need a lot higher force to release from the trackies than the roadies. The shimano's are harder to get out of, but like I mentioned earlier, no accidental releases with either system.
So, if it's a locked in feeling that you value, go with the shimano. If it's free float that you value go with the speedplay. Either system, the X or the Zero is good for someone your size, with the X's being slightly better. Neither brand will accidentally release you, and you won't need a toe clip with either pedal if you use a decent laminated strap.