5" is 'okay' on an 8" rim. Sure it's more sucked in than people like, but it's still pushed out about an inch past stock sucked in crap. And it's got way more aggressive tires on it making it look bigger and better. But the tires will still be entirely inside the fenders/flares.
Here's a pic of my buddy's old truck.....16x8 w/ 5" bs on 305/70R16's (and a superlift)
In regards to getting 10's....I wouldn't. 10's don't typically agree with non-lifted trucks and sheet metal.
Are you dead set on 16's?? Because you can fit 15's easy AND tires are way cheaper. Plus, they'll be rated correctly for the truck. AND you can get 15's in much more desirable backspacing. Look into 32x11.50's and 15x8" rims with 3.5-4" backspace. This will put the tires even with the flares and a very mean looking stance without being overly stupid sticking way out the fenders.
In fact, here's my truck back in the day with that exact setup: 32x11.50 BFG's on 15x8's w/ 4" and a slight torsion crank....