I'd guess we'd keep a 5M cushion minimum for in-season injuries.
Awhile back I did some research to address the claims of a Colts fan who said that in part they were limited by being a small market team and paying at the low end of the salary spectrum, even though the range of salaries in the NFL is rather small due to the hard cap.
I thought I'd share those results here, gleaned from the USA Today site which has historical salary figures from 2000-2009 (nothing for the uncapped year).
2009-10 NFL Salaries by Team - USATODAY.com
Not surprisingly, there is a poor correlation of salary spent with success.
2009 Patriots were 25th in payroll. Colts were 19th in payroll. Saints (4th) won.
2008 Patriots were 30th in payroll. Colts were 29th in payroll. Steelers (6th) won.
2007 Patriots were 2nd in payroll. Colts were 12th in payroll. Giants (32nd) won.
2006 Patriots were 12th in payroll. Colts were 1st in payroll & won
2005 Patriots were 7th in payroll. Colts were 23rd in payroll. Steelers (10th) won.
2004 Patriots were 24th in payroll and won. Colts were 8th in payroll.
2003 Patriots (9th in payroll) won. Colts were 23rd in payroll.
2002 Patriots were 31st in payroll. Colts were 15th in payroll. Tampa Bay (16th) won.
2001 Patriots (23rd in payroll) won. Colts were 24th in payroll.
2000 Patriots were 25th in payroll. Colts were 17th in payroll. Ravens won (13th).
So for a ten year period (the total of the USA Today database)
The Patriots were on average #19 in the NFL in payroll
The Colts were on average #17 in the NFL in payroll
The NFL champion was on average #14 in the NFL in payroll
bottom line: I seem some random fluctuations, two fairly frugal teams, not really indicating any inability of Indy to pay salaries necessary to contend.
Look at the top salaried teams though. More often than not, they did not even make the playoffs.
Also, paying high salaries in the NFL doesn't mean you have better players. It means you have made some awful mistakes in giving out some lousy contracts, then often had to scramble to cover up holes left over by overpaying other guys as well, and even pull some cap shenanigans to accomplish it, which hurts the team in the long run.
Consistently well-run teams seem to thrive in the 10-20 zone of salaries paid out.