So much more to the GVWR than just the springs and tires. What will you do about frame, steering, brakes, suspension joints, ..... ask Toyota if going over their GVWR will affect warranty.
I've seen a Ram go into a dealership while on vacation with a broken front knuckle u-joint. The dealer scaled the truck and formally voided the warranty.
FWIW, the Tundra is somewhat over-engineered and underrated as it comes from the factory. Toyota lent an unmodified Tundra to a ranching operation where it was pulling +12k lb cattle trailers and performing general ranch duties on rough roads for 100k miles. Didn't seem to cause any undue wear. The Toyota engineers obviously stated that they don't condone going over the tow ratings, but that they weren't surprised the truck fared as well as it did.
That aside, I agree with the above post: there is more to GVWR than springs and tires. I don't know what the OP has on his Tundra so that it is already within 100-200lbs of GVWR. If you need to exceed that 1.5-1.6k payload on a frequent basis, I'd heavily consider getting a 3/4 ton.
For suspension, I'd take OME (either the old nitrochargers or the newer BP-51's) in a heartbeat over anything else. ICON makes very capable suspension setups, and I'm sure they last for a while. OME still has a better reputation for reliability and longevity. The tradeoff is that OME won't have the same degree of comfort and ride compliance as a high-end ICON kit (at least according to those who've done direct comparisons). I'd trade a little bit of comfort for better reliability.
