I don't think this is true: "The team trading for Gurley needs to eat the yearly salary plus the non-amortized portion of the bonus (8.4 per year). Same result for either team regardless if he is kept or traded."
As far as I know if the Rams trade Gurley all non-amortized bonus money goes against the Rams cap when the trade happens. His new team wouldn't have to account for his signing bonus at all.
And according to overthecap.com it's $4.2M a year. Trading Gurley now accelerates the pro-rated signing bonus money from 2021 and 2022 to this year, a total of $8.4M. If Gurley plays for the Rams in 2020 his cap hit is $17.25M. If the Rams trade him his cap hit is $26.65M. [
overthecap.com]
AlbaNY_Ram