I would only go out 4 years initially. If after 2 years the program was trending up I would give him an extension. Six years out of the box concerns me, but maybe I am the only one concerned about the length of the contract.
If Purdue had been winning B1G West titles and had been in the top 25 year after year, and was considered somewhat of a desirable destination, then a 4-5 year contract might have been within negotiation for a coach coming from the Group of 5.
But we are not. Consider:
1) we have not had a winning season since Tiller,
2) two coaches since Tiller have been hired and fired,
3) our recruiting has been abysmal,
4) we traditionally have issues trying to recruit top players, even in the immediate area,
5) the athletic department has a bad rep, nationwide, of being cheap with minimal commitments, and
6) we have no proven brand. In fact, the NYT said we "fancy ourselves the 'Cradle of Quarterbacks'" as opposed to Purdue IS the Cradle of Quarterbacks. And they only mentioned Len Dawson, Jim Everett, and Brees - no mention of Griese, Danielson, or even Orton. In other words, several schools have had much better QBs come out since the last significant one we produced. Not much of a cradle anymore, sorry.
The bottom line is that the program is one of the worst Power 5 jobs in the country, and it will take several years to turn the ship around and make it a winning program.
And because of that, no respectable, promising young coach is going to accept a minimum 4 year contract with the risk he could permanently damage his career in that short of time frame. Actually, I am surprised that we got Brohm for less than an 8 year commitment. And I am thrilled we got someone who has a real track record for at least six years - because it may very well take that long.