The big main ability I think would be the best to create a fairly unique Pokemon for mixed boosting. Prankster.
With Prankster you have priority boosting, and even bigger, potential priority recovery.
A Pokemon can be far more bulky with the ability to guarantee recovery first.
It would also...
With the right set up move you don't need particularly high stats. Just as an example, Serperior manages to be a threat (just barely missing OU by 0.3% points) with just 75 SpA. Granted, for it the "right set up move" is a 130 BP STAB attack but the point stands.
If we don't want the CAP to...
I'm surprised that nobody's brought up Nasty Plot + Bulk Up/Coil.
First, consider Bulk Up. There's a lot more physical sweepers/revenge killers out there, thanks primarily to the bulk of priority being Physical. Defense boosting would allow the CAP to better shield themselves against these...
I think the baseline of 33/65 is fine.
As is Volkraken is going to have 4MSS since it's going to need both it's stabs and at least one support move already. Letting it have more then a handful of options for the fourth slot isn't going to hurt it and allow it to do its job much better.
Disallow Flame Charge
CAP has the power to be able to do massive damage with just a speed boost, in fact;
Disallow Thunder Wave
The CAP already is spreading burns and is specially bulky enough to handle most Special Attackers. Plus, you know, speed.
Allow Yawn/Roar/Whirlwind/Perish Song