I can't say how the VA stacks with the TST, but I've read about several members liking it. The VA is all low end, so it may or may not have a smooth transition (in relation to where the TST comes in). The TST ramps fueling from 12 to 28-30psi, so depending on where you are in the rev range, it may not make a smooth transition.
I dynoed with my TST/BDDL stack and got the numbers in my sig. I used the TST on 7x7 and the BDDL on tow. It runs really well like that. In fact, the BDDL is a good smooth power adder, and though I'm disappointed I cannot get a Crazy Larry for my truck, it seems the best stack is the tow mode. I let the TST do the rest. Smooth power, any time.
Now I have the "early twins" flash on my TST. It's not so smoky by itself until you turn it up too high, but put the BDDL on tow and look out! Smoke city. Gotta be a little careful sometimes. It's a whole lot of fun, though.