Well the first question is why is it sticking, if indeed it is. Any sign of overheating? Has the car been subjected to cheap oil that's coked up on the valve stems? I've seen carbon deposits from cheap gas wreak havoc on a couple of 850 valvetrains, and if you're a particularly pedestrian driver (ie, never over 3500rpm) that driving style doesn't do the engine any good. I know of mechanics who swear by various fuel additives for carbon removal. Also do a search here for info on seafoam treatment (both pros and cons). Switching to good-quality synth oil like Mobil 1 will gradually help clean up carbon deposits including in the valve guides. If possible do a compression test when the engine is acting up to verify if it's indeed a sticking valve, you should have lower compression in the offending cylinder. That would explain the ticking, as the cam lobe hammers against the partially-depressed follower instead of gliding across it, as well as power loss.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina