The Pegasus is Nike's longest-running road trainer, and the 42 is the current one. The change is underfoot: a curved Air Zoom unit now runs the full length of the shoe beneath the same ReactX foam, so more of each stride comes back than in the 41. Under a 10 mm drop, the brief stays what it has always been.
It suits you if you have bought Pegasus for years and want the same easy-and-long shoe with a livelier forefoot, or if you want a first dependable trainer and would rather not think about it again for a season.
It is not a racing shoe, and the Air unit does not change that. There is no plate, and at roughly 300 g a hard 5K will feel like work. It is not a trail shoe either: road rubber lets go the moment the ground turns wet or loose.