The attack speed bonus from swf affects everything. So a more precise calculation would assume 20 attacks for swf, multiply that result by all sources of doublestrike including gear, feats, enhancements, EDs, etc. (for both swf and twf), and
then multiply the result by 1.3 for swf. Based on that alone, swf will definitely pull ahead, but by how much is the question.
It's difficult to calculate the exact doublestrike bonus from zeal of the righteous since it decays over time. Like Caprice, there was a time when I could have done such math. Use it or lose it I guess.
But assuming you keep it on cooldown, then there would be a definite average doublestrike that it adds.
EDIT: Base doublestrike for each would be:
SWF:
2 swashbuckler cores
15 legendary shield mastery (10 from swashbuckler if no shield)
5 ptwf
10 celestial fervor (gain 1 doublestrike on crit, easy to keep up on a build with a high crit rate, does not stack with items)
32 total (27 if not using a shield)
TWF:
5 ptwf
10 celestial fervor
15 total
Each could potentially have 1-4 more from eldritch knight depending on how enhancements are spent, but this shouldn't make too much of a difference. 1 is easy and cheap since it's the first core, but I wouldn't count on the other 3.
EDIT EDIT: Also, since Caprice did a simulation based on millions of trials, I would be using the 48.4% crit chance from that, not 50%. again, a minor difference, but since the result is close already, these will determine which one is actually higher.
And based off of the rough calculations I just did, which may or may not be correct, zeal adds an average of 4.72 doublestrike.