What size tires on stock 20's?

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I found some 20's for my 2wd 05 GMC CCSB. They're the factory 6 spoke GMC wheels. The question is what size tires to run? The stock size for these is 275/55/20, but I think they look a bit too beefy on a 2wd. I want to go with something a bit lower profile because I may lower the truck 2/4 sometime in the future. I was thinking either 275/50/20 or 295/45/20. Will the 295/45 fit on the stock wheels?

Below is a pic of a truck like mine with the wheels I found. I don't plan to go that low, though.