If it's already going to be an SBR, go for the 53. I have a 53 I built from a 93 and an all German 53 kit. It runs flawlessly, with and without a sear. The recoil won't be noticeably different, and it's still only a 5.56 anyways. It's not going to be close to a .308. Accuracy depends more on whether or not you have a scope on it than barrel length. The longer sight radius of the 93 will make it only very slightly more accurate with the aperture sights, but put a scope on it and they'll both be as accurate as YOU are. I don't have a 33K, but I have a 91, and a G3K, and they both shoot about the same, and the barrel length differences will be the same as the 93k vs 53. Anecdotal - I almost always take my 53 when we go shooting. I haven't taken a 93 out since I built the 53.