Yes, I think flats provide a huge boost. Prior to a race, there’s nothing better than doing your warmup in a pair of trainers then lacing up a pair of racing flats. In addition to the lighter weight, the psychological boost is huge too.
Also, is a marathon to long for flats?
It depends on the person. Personally, I like a pair of light weight trainers for the marathon. These shoes probably by between 9-10 oz, whereas flats are closer to 7 oz.
I think another reason the elites can “get away with it” is because they are biomechanically efficient.
Will I really save time or will my feet hurt enough to slow me down too much?
During a marathon, flats will probably save you some time early on, however in the long run (pun intended), you’ll be worse off. It’s not just your feet that hurt, it travels all the way up your legs.
Do you know which racing flat you have? What are your trainers?