I'm in AGNC with 4,914 Call Options...let's Rock n Roll : )
I think Dec is the better play for what X desires which is greater leverage. Secondly, AGNC has been moving their EX dates forward, meaning that , I believe, the EX will be @ the Dec OPEX or one to two trading days earlier, so the run should be over , or close, by Dec OPEX.
You left out a very important component in your cf of the Dec to the Jan contracts. The # of contracts X can purchase given a limited amount of money(in this case almost 500k). Watch:
When X bought the Dec 31s ,trading for 1.00 avg, the Jan 31s were trading for 1.14. Lets say he had 400k for that trade. He would be able to get 4,000 contracts(ignoring commission) in Dec and 3,508 contracts of the Jan.
PPS goes to 33.00 @ EX and the pot doubles on the Decs for 400k profit and there is still .20 bid left on the Jans(2.20 bid) which gives you 2.20 x 3508 or 372k profit.(28k difference). (I got these values looking back @ Oct 2012 OPEX which was 33.00 PPS close, and used the 31.00 Strikes for Oct and Nov as proxy).
Furthermore suppose we go to 34+(my thought) and the EX is B4 the OPEX(my thought), and X is still holding. Then the difference between the Jan contract and the Dec contract is only 7 cents(bid). Now he makes( at 34), 792,000 profit , whereas the Jan makes 669,940 profit , or a 122,060 difference.
The benefit, of course of the Jan over the Dec is if we don't make BE(32) by Dec OPEX or EX.