What happens when you put vortex generators on both sides of a symmetrical vertical tail? What happens when you put vortex generators (VGs) on both sides of a symmetrical vertical tail?

I understand a horizontal tail with a classic foil like a NACA 0012 has a max cl of about 1.5.

I understand VGs add about 0.6cl.

What happens when you put VGs on both sides of the vertical tail?

For sure it will allow lower speed or better control at lower speeds, but will it actually bump the max cl from 1.5 to 2.1 at positive and negative angles of attack?

That's a 40 % increase in performance!!! 

So.... can I decrease my vertical tail by roughly 40% and still get a similar EFFECTIVE vertical tail volume ( vertical tail moment)?
Just because VGs can delay the flow separation (with no guarantee of success), it doesn't mean you have increased your tail volume. In fact, you have the exact same tail volume unless your vertical tail is separating at small sideslip, which probably indicates bad design or bad manufacturing.

If the VGs do increase the max Cl, it means you may be able get to a higher slip angle, perhaps more crosswind capability if your rudder is up to the task.