It is not LIKELY to make any ACTUAL difference at all. If you tow a 10,000 lb. trailer it will more than likely overload the payload capacity of your Tundra anyway, making it unsafe to actually tow it. The new max trailer size is much more likely to leave the payload able to handle it.
I"d forget about any 20% cushion as that is just plane bunk. Maximum trailer weight is not even a SAFETY related issue, it merely tells you at what point the manufacturer has an "out" if you have a warranty issue. If you're towing more than their specifications say they don't HAVE to honor warranty for weight related issues. The numbers you should be VERY particular about are the GVWR and GAWR of your truck as THOSE are safety related issues (required by federal law to be available on your DOT safety plate, mounted on your trucks door post).
Good luck / Skip
