This discussion got me thinking and I looked up some numbers. If I had to do it all over again, and had a bigger budget, I probably would go to 17" rims to give me more options than E-rated LT tires. The 285/75R16 E's I have on my stock OR rims are stiff, heavy, and my mileage did decrease. But they are extremely beefy and have handled everything I've thrown at them. BUT a C load rating is more in line with what the Xterras weigh and does result in substantial unsprung weight savings, potentially. And the cost is only slightly higher it seems going from 16 to 17 rims nowadays. For comparison using BFGoodrich KO2s at load C, versus E vs stock Rugged Trails, numbers rounded from what I've seen listed on this site, or manufacturers sites:
Stock OR 16 x 7 wheels w/ OEM Rugged Trails total weight = 66 lbs (265/75/R16 P)
Stock OR 16 x 7 wheels w/33" KO2s in Load Range E = 85 lbs
Stock steel wheels 16 x 7 w/ OEM Rugged Trails total weight = 89 lbs
Stock Steel wheels 16 x 7 w/33" KO2s in Load Range E = 101 lbs (285/75/R16 E)
NISMO 17" x 7.5 wheels w/33" KO2s in Load Range C = 74.8 lbs (285/70/R17 C)
NISMO 17" x 7.5 wheels w/33" KO2s in Load Range E = 82 lbs (285/70/R17 E)
The MSRP cost difference between 33" KO2s in 16 vs 17" rims when I looked it up was only $251 vs $267 each, in load E and C, respectively. For E and E, it's $251 vs $278. But then you have to buy 4-5 wheels on top of that.
You can also shave off a few pounds of weight going with NISMO or other alloy wheels. Going from a P-rated OEM tire/wheel combo to a 17" LT-C rated tire/wheel combo might only increase the weight by 9-10 lbs. And "officially" 285s usually require 7.5" rim width, versus 7" that the stock wheels have but we run anyways. And it's pretty obvious why running steel wheels and heavy, bigger LT tires kills gas mileage and noticably impacts the ride--you can easily exceed 100 pounds on each corner unsprung weight.