It's OK to use a yoke style K valve on a high pressure tank up to 4000 psi. In the 1970's, US Divers rated their yokes at 4000 psi working with failure limit of 10,000 psi, and this is the same yoke in production today. Personally, I set 3500 as the working press (my compressor relief valve won't go any higher). Look closely at a modern yoke, especially Scubapro and USD; these are strong enough to use as a trailer hitch. Don't worry about that. It will never break due to tank pressure. If the valve is new or otherwise in good condition and the O ring is the white, hard silicone type, the ring will never blow out. You see, also in the 1970's, coincident with the yoke redesign, Sherwood Co. completely redesigned the valve annulus which seats the O ring. That interface is no longer a compression fit where the ring acts as a washer. The fit is a 'semi captured' design which makes metal to metal contact between the regulator and valve face. The O ring CAN NOT BLOW OUT unless the annulus has been icepick challenged. Relax and don't pay any attention to all the reasoned 'arguments'. I've been there done that.