OEM is going to be one year warranty vs 3years and could be a crappy bin, which means you may get crap or an inability to do overclocking which with a K processor you probably want to do at some stage. This is a decent processor but it has less threads and the performance vs the ryzen 2700x is around the 10% less in anything but 1080p. The 2700x is £100 less and comes with a good standard stock cooler. When you consider that this is OEM with a lot less warranty and a possibly inferior version then there is not much "deal" about this price. So you could save £50-£60 but end up with a crappy £400 processor with no protection after a year. You have to decide whether that's worth it or not.
From what I've seen, Ryzen just doesn't perform that well for gaming - a primary use case for me. Until AMD fixes this, I'm still not entertained by what AMD has to offer anymore. I used to be a big AMD fan but since switching to Intel, bottlenecking etc I've found has just gone away. Price to performance, Ryzen is amazing value and they've done very well to bring themselves back up to speed out of no-where. If I was someone who dealt with video editing or similar, where the Ryzen outshines the Intel family, I'd be more interested but sadly, the benchmarks show AMD still have something to prove within gaming. That and well, I plan to Hackintosh and I don't really want to deal with endless hickups with AMD and MacOS. It still baffles me why AMD haven't just announced their Navi line-up and are still trying to push an architecture that is 2 years old.
It's a good CPU but very expensive for gaming, 9600k is equally fast. But r5 2700 is best value just wait for price drop.