Well, here's my opinion: Get the bigger tires. If you are actually taking it offroad, bigger tires have multiple benefits. 1) Larger tire = smaller bumps/holes/gaps, etc due to the increased rollout. 2) Larger tire = more capability. Bigger footprint will improve performance offroad particularly in soft ground: sand, mud, etc. 3) Suspension improvement. The sidewall of a tire is an integral part of your suspension and it's performance capabilities. Bigger tire = bigger sidewall = more shock absorption. 4) 3/4" of additional clearance actually is a big deal when doing things where space and clearance count. As already mentioned, there are many more factors to consider than just clearance under the differentials. 5) Do NOT go bigger than an 18" wheel (see previous comment on sidewall). Not to mention, a higher probability of bending/breaking the actual wheel. 5) Keep the offset at or near stock (should be +0 or in that area). Big offset = substantially increased force on your already way too small tie rod ends. +0 offset will also allow the tire to rise into your fenderwell on compression, rather than hitting the outside of the fender. 6) Level it. If you're Silverado is like my 02 Avalanche, the forward rake is very limiting when talking offroad capability as it seriously degrades your approach angle. I leveled mine 2" in the front. Combined with cutting the front bumper and fabbing a tube bumper - I gained 14.5" of front approach angle. When I put 285/70-17 on my Av (+0 offset wheel), I did some very minor trimming. When I just put the 35x12.50-17 on my Avalanche, I did substantial trimming (fenderwells, cladding, firewall) - BUT every kit manufacturer told me I HAD to put a 6.5" lift on my Av to fit 35" tires. Um, wrong.....................Just be honest with yourself, how do you want to use your truck? Then, start setting it up to do that - reliably. You should buy the Rare Parts 1.5" tie rods as a priority when adding bigger tires, OR taking it offroad. As for tread, there are a lot of options between a pure street tread and a mud terrain. Our trucks are heavy, get something in an E rating, your sidewalls will thank you.