I like to make choices so that failure still results in some measure of improvement.
I originally got back to into sprinting 18 months ago to get back in shape and see if I could beat my old PRs. I wanted to run 10.4. I haven't come close since deciding to train again, in fact i've only been sub 11 once in the last year. Still... compared to a year ago my life is immeasurably better thanks to sprinting. I'm 30 pounds lighter and I can step on the field and play a mean game of flag football or soccer. The general increase to my athleticism is amazing, even if I haven't rediscovered what my definition of success is as a 100m sprinter....
That's why I favor the decathalon over powerlifting. Sure you might become a powerlifting champ. But if not you will be an overweight fat looking guy who can lift a decent amount of iron but can't chase his kids around the house because he get's out of breath too quickly!
You also might not be a great decathalete. But you will have a remarkable level of general fitness, learn all kids of new skills like hurdling, javelin, running and be able to beat your avg guy in a sprint, a middle distance race, and a long race. You will be able to enjoy team sports and recreation much better and be healthier for it.
Sorry, to get on the soapbox. Obviously, I'm a big fan of track and field. But there is a reason why you guy's call it athletics in Europe! It's the mother of all sport. And the decathalon is the granddaddy of all events. Also, you are lucky if you currently have access to all the implements (ie. hurdles, pole vault, etc.)... If I had access I'd probably train to be a decathlete too! Powerlifting equipement is much easier to come by!