As for the pressure, w/o knowing what Make & Model you have, my Advisors can't advise. BUT, they suggest you get this info anyway and ctc the mfgr.
As for the relief valve, go ahead and drain the tank. If the valve still leaks after draining, then the valve is bad. BUT, if it doesn't leak after draining, you should be OK. In any persistent leaking situation, the relief valve is your fail-safe. Do be sure that your 'tests' don't show a persistant leak. If so, change it. If you must, have a pro do it if you can't afford the downtime.