Are you talking about the 5600 XT Pulse or the RX 560 Pulse? Either way it shouldn't really matter, as both of those cards do have idle fan stop. Maybe you had a program like Afterburner interfering with it or something. I assume you probably mean the RX 560 by the missing shaders comment, but that was an AMD thing in general rather than anything Sapphire did. They made the choice to sell two different versions of the RX 560 with different shader counts whilst naming them identically. As for crashes, that could be anything from a faulty card to a problem with your setup. Nothing to do with the model of card though.
The Pulse lineup in general have been fantastic cards. I had the Vega 56 Pulse and it was great, and from all the reviews so far it seems like the Pulse is one of the best 6600 XTs. Haven't found any reviews of the Nitro, but it seems to be pretty much exactly the same card with some RGB nonsense for your extra £25.