Switch now, use them for your hard workouts (intervals, tempo, and the like), and racing. Don't use them for your plodding recovery runs, as they won't really work and you're wasting expensive shoes. Yes, you'll be faster, but as sibling says the real benefit is your legs don't get as trashed on hard runs.
They will last longer than advertised. yeah, I probably wouldn't race marathons in them much past 200 miles or so, but I've got some Vaporflys that I only use for workouts now, and they are approaching 400 mile, IIRC. I've done back-to-back comparisons with the worn pair and a practically new pair, and yes, they lose a fair bit of bounce after 200 miles. But they can still be used for workouts, and they still preserve the legs.