I appreciate all the work crunching numbers but I disagree with your numbers. Normally Shamsports is a better source of salary numbers.
https://www.shamsports.com/content/pages/data/salaries/thunder.jsp
First of all, according to Shamsports in 2013/2014 Ibaka and Harden are RFA. Neither of them would hit the open market until 2014/2015. Meaning you would have to offer Ibaka very close to a max deal. It also means that if Harden his the free agent market he would likely be offered a max deal.
The salary cap for 2011/2012 is $58,044,000. Luxury Tax is $70,307,000.
In 2013/2014 the Thunder has these players under contract:
Player 2013/2014
Kevin Durant $17,832,627.00
Kendrick Perkins $8,477,437.00
Russell Westbrook $13,891,359.00
Thabo Sefolosha $3,900,000.00
Nick Collison $2,585,668.00
Cole Aldrich $3,245,152.00
Reggie Jackson $1,260,360.00
Lazar Hayward $2,119,214.00
Total
$53,311,817.00
That is eight players under contract.
So they would be $16,995,183 short of the 2011/2012 luxury tax.
Lets take a guess that the luxury tax will increase 2.5 mil/year. So the 2013/2014 luxury tax number would be $75,307,000. Meaning the Thunder would have $21,995,183 to sign Harden and Ibaka and feel out their roster.
If Harden is a max extend player he under 2011/2012 the max for a player with 0-6 years of service is $12,992,194. The 5 mil increase in the luxury tax is a 7.112% increase. Assuming the max deal would go up to $13,916,155.6.
In theory then with 9 players the Thunder would be $8,079,027 under the cap.
Say they can sign Ibaka to a 12 mil/year contract.
That is a little over 4 mil above the projected luxury tax level with 10 players. To reach the required 13, let's assume an average 1.5 mil/year for the other 3 players. So adding a total of 4.5 mil the Thunder are a total of 8.5 mil over the projected luxury tax.
Perkins contract ends in 2014/2015. The Thunder could bite the bullet and play the luxury tax for a couple of years so they could keep their big four together and be about 9 mil over the luxury tax.
If they amnesty Perkins they would very, very close to the luxury tax level.
IMO if they think Ibaka, Harden, Durant and Westbrook are a championship level core I don't see them breaking up that team. And it wouldn't be ridiculously expensive to keep all four.