I've still never seen any math where a withholding attack doesn't cost you more than it provides.  If you have 10 PH/s, the network is 100 PH/s (including you), and you do a withholding attack on a pool with 20 PH/s.  Okay, so now you have effectively removed your 10 PH/s from the network, so the difficulty won't reflect your speed.  However, in the course of doing that (effectively reducing the next difficulty by 10%) you're taking a HUGE cut in your pay.  You'd be earning 33% less than expectation (you would be 1/3rd of that originally 20 PH/s pool, and by withholding that pool will under-perform by 33%).

I've played with the numbers endlessly, and the result is always the same.  You cannot perform a withholding attack where you end up earning more are higher than they would be if you were legitimately mining at 100% capacity.  It's the simple fact that you can not make the network difficulty be adjusted by more than the pay cut you're taking by performing the attack.

Now, this obviously only applies to non-PPS pools.  With PPS it's completely viable to do withholding attacks because your earnings hit is only the pool fee whether you are solving blocks or not.  Your only problem there is making sure you are able to continue pulling your balance out before the pool goes bankrupt.

The only impact that such an attack would have is to try to ruin the pool, or to earn BTC without impacting the difficulty.  (Which, granted, could be goals of an attacker.)  But the attacker could not *gain* anything by such an attack.  Their 10% would earn just as much BTC by solo mining as they get in the pool; and the other 10% would not earn any more or less.