Adizero Prime X 2 vs FuelCell SuperComp Elite 5

With 50mm under the heel, the Adizero Prime X 2 sits a full 10mm over the World Athletics limit for road racing, so no record or championship result run in it will stand. adidas built it that way on purpose, as a carbon-plated experiment in how far stack can go, and most reviewers ended up treating it as a very expensive super trainer rather than a racer. The softness won nearly all of them over. The weight was a different story: it put on a lot over the first Prime X, and several testers struggled to hold faster paces in it. Lab testing and two of the reviews rate it well for long runs and marathon-pace sessions, while one US panel called it a step backwards and preferred version 1. Coach's UK review lands in the middle, calling it great fun but priced above legal racers that do the job better. If you want an adidas marathon shoe for race day, the Adios Pro 5 is lighter, cheaper and legal. We'd buy the Prime X 2 for how it feels on long miles, and only once the price has dropped.

The FuelCell SuperComp Elite v5 is New Balance at its most serious: a carbon marathon racing shoe built to chase a personal best on the road and nothing else. This is a full super-shoe, with a PEBA midsole and a carbon plate that New Balance says is 38 per cent stiffer than before, and at 213g it is genuinely light for a shoe carrying this much foam. That combination is the whole point. You get a tall, energetic stack that protects your legs deep into a marathon, and a plate rigid enough to snap you onto your toes when you hold race pace. It sits right at the top of the road racing market on price at 220 pounds, up against the Nike Vaporfly 4 and the rest of the carbon crowd. We rate it as a true race-day tool. It rewards a committed effort and feels flat if you jog. Buy it to race, not to train.