TLDR: Exploit Weakness gives Picks a much bigger boost than non-Picks. You should use a Pick for your TF if you're a Swashbuckler
I ran a computer model to see how much Exploit Weakness was actually granting in terms of "effective crit threat bonus", and I thought I'd post my results, if only so I have a record of it for myself . Maybe someone with a bit more stats knowledge than me has already figured this out symbolically, but here's what I found:
Non-picks (all 18-20/x3 with Swashbuckler), each non-crit adding 10% chance to the next swing until a crit occurs:
Base crit range (18-20) with Imp Crit: No EW, 30% crit; with EW, 40% crit, effectively +1 crit
Expanded crit (17-20) with IC: No EW, 40% crit; with EW, 48% crit, effectively +0.8 crit
Double expanded crit (16-20) with IC: 50% without, 56% with, effectively +0.6 crit **dunno if a double-expanded Swash weapon actually exists or not
Base with Picks (19-20) with Imp Crit: 20% without, 34% with, effectively +1.4 crit
Not that any Swashbuckler *wouldn't* take EW, but that gives you an idea about how much its worth.
Now, considering Picks vs Non-Picks for Swashbucklers:
Picks: 34% at x4 =300*0.34=102% bonus damage
Non-picks: 40% at x3=200*0.4=80% bonus damage
Expanded non-picks: 48% at x3 = 200*0.48=96% bonus damage
Since Light Picks gain significantly more from Exploit Weakness than non-Picks, the net DPS bonus is greater for a Light Pick than even an expanded non-Pick. This is *not* what you'd find if you just considered the raw crit profiles, unboosted by EW, where 20%/x4 comes out the same as 30%/x3
What does this mean? Well, when choosing a weapon for a Swashbuckler - all things else being equal - a Pick is preferable to anything else. So if you're rolling a TF (or a Cormyrian) weapon for your Swash, you're going to want a Light Pick. Since there are no named Light Picks, that's probably the only scenario that actually applies right now. Assuming, of course, you have IC:Piercing and not Slashing or Bludgeon.
"But Light Pick has lower damage dice, 1d4 vs 1d6!" Yes, but when you're applying double stat bonus to your attacks, plus all the other sources of flat +damage that get multiplied by your crits, the extra 4.5 points difference in base damage between 4.5[1d4] and 4.5[1d6] are negligible compared to the 22% difference in bonus damage. Unless you had significant +damage bonuses associated with a certain non-Pick (racial, favored weapon, etc.), you should probably still go with Pick.
Disclaimer: my interpretations and analyses are based on my numbers...so if you don't believe them, don't believe anything else, but tell me where I'm wrong