Depends on what that $6.7M means. Is that salary and bonuses? This will be his last big check and I'm betting he'll want $20M up front to sign for 4. Puts his cap hit at $10M if he's getting $6 per for salary and incentives.
Here's some comparisons between him and Cobb. Graham hit Seattle's cap for $10M in 2017. Cobb was $12.7M in 2017. Cobb(27) is 4 years younger than Graham(31).
Tgts Rec Yds AVG TD Lng RPG YPG Ctch%
96 57 520 9.1 10 33 3.6 32.5 59.4% - Graham
92 66 653 9.9 4 46 4.4 43.5 71.7% - Cobb
This is with Bart Hundler at QB vs RusWill. Not sure what you're gaining at that point.
Edit:
Nelson plays outside, but here's a comparison just for fun.
Nelson(32) hit GB's cap for $12.5M in 2017 and is a year older than Graham
Tgts Rec Yds AVG TD Lng RPG YPG Ctch%
88 53 482 9.1 6 58 3.5 32.1 60.2%