A 'solid 4-8 years' is a ridiculously high bar to set for a late 1st round pick.
The average 29th pick has a CAV (Career Approximate Value) of 30. That's Lawrence Maroney. Getting a good starter for 4-8 years is a resounding success late in the first round.
Well there have been a fair number of them -- including Ryan Pickett (14 years), Marc Columbo (11 years), Nick Barnett (11 also), Michael Jenkins (9 years), Nick Mangold (10 years and counting), Ben Grubbs (9 years and counting), Hakim Nicks (7 years), Kyle Wilson (6), Harrison Smith (4 and counting).
Arbitrarily, I quickly checked the 16 players selected at 29 in the first round since 2000. Put aside for these purposes guys selected from 2013 forward who could not yet have 4 years in the League -- Phillip Dorsett (Colts, last year), Easley (Pats 2014), Cordarelle Patterson (Vikes 2013); you can argue they are too new. Easley is the only one from this group to be jettisoned.
You'll find in this group of sixteen 3 guys who plainly busted -- R.J. Soward, Jags, 2000; Kentwan Balmer, 49ers, 2008; Gabe Carini, Bears, 2011. All the others had at least 4-year careers -- and Harrison Smith is "and counting". The range for the others players goes from 5 to 14 years.
Seven guys drafted at 29 had at least 5 years with the team that drafted them, and all but one of them moved on to continue their careers elsewhere.
So if you count the bust rate at 25%, we clearly hit that with Easley from our standpoint. And a good number of the other ones have had nice careers.