Lighter is not always better. For competitive runners who are used to running barefoot, barefoot is faster than with shoes. For 200 pounders and runners who are used to jogging on their heels it probably doesn't make any difference.
A top runner is not always better served by lighter shoes. The design of the shoe is also extremely important. There area many ridiculous 5oz shoe designs. For one thing, the great majority of racing shoes have built up soft midsoles, which is totally ridiculous.
I think you should wear the heaviest shoes you can find.
Americans are usually much heavier than Kenyans, and slower. Wearing lighter shoes is not going to make as much difference to heavier runners, as I pointed out previously. Why are American marathon runners so much slower now than they were in the 1970's when everyone was wearing minimalist shoes? Huh there's a question for you.