I'd seriously consider the max. Not because it's his ideal price, but there are a lot of factors working in that deal's favor:
1) His max is relatively lower due to years experience
2) This summer is a good time to lock players up before the cap goes insane next summer. His contract won't look so expensive when someone gets $35M/year
3) He's 26 and healthy
4) We have the coaching talent to utilize unique weapons like Whiteside
5) He performed in the playoffs
6) He improved his free throws
7) Great perimeter defense + great shotblocking could be a lethal combo, even if Whiteside isn't a great team defender

His raw numbers are All-Star level. I'm definitely an advanced stats guy, but 14/12/4 on 9 shots and no need to call plays for him is hard to deny
9) We have the money - unless there's a clearly better option, spending it on a very high upside guy makes some sense