I have some custom lightweight Cataracts and a pair of Sawyers Square Tops with Dynelite blades. No complaints with the Cataracts, but the Square Tops are in a total class by themselves. IME, rowers of all levels can appreciate the difference.
Can't comment on durability of Razors, but the Dynelites seem more durable than my Magnums, which are not only heavier, but softer too. The Razor blades aren't cheap, but if you are looking for lighter, stiffer more durable blades like the Dynelites without having to buy the farm, get the Razors and keep the Magnums for back up. Replaceable blades are a nice advantage on the Cats. It might even be possible to get Dynelites that fit your Cats. Give Sawyers a call; Bruce has always been straight with me. The Dynelite blades on the ST's are factory replaceable only, a negative especially given the 9' UPS limit. But having said that, my Cats have been collecting dust ever since I got the ST's. They are that good. If you go Sawyer for Dynelite blades, I would not hesitate to look right past MSXG to the ST's.