Does anyone have the VA duration box on a 305 with intake and exhaust? That experiment is in my future, to see if air gives us much relief in the EGT department. Other than that, I'm still in favor of stacking the VA duration box with a pressure box -- that gives you some relief from the EGT problem with duration alone, and with air mods on a 305 it might be workable. I'm afraid I don't have experience with the 600.
As an aside, if you follow Edge's lead in the pressure department, you shouldn't add more than about 70 HP with pressure only. So if you don't want to add injectors, the only way to go above 70 HP is with a duration box. and the only two choices now are TST and VA -- TST being a more risky choice if you keep your stock turbocharger. The VA runs hot, but it does not hit the turbo nearly as hard. The flip side of that problem is that if you go above 70 HP you need to upgrade your turbocharger anyway, at least if you plan to utilize that HP in a sustained towing situation and not just a quick flash in the pan race or dyno run. Again, my experience and observations with the 305, not the 600.
I learned very early on in my VA experience that best results are obtained with the VA duration box turned down to level 1 and a stacked pressure box of your choice, including of course the VA pressure box.
As regards the 600, I would imagine that this puppy would run hotter with the VA than the 305, simply due to the fact that timing is already heavily retarded comparatively. So that means the worst possible EGT problem would occur on a stock 600. As I say, the data isn't all in yet on the 305 with intake and exhaust, fitted with ~ 50 HP worth of presssure and the VA duration box turned down to level 1. The pressure alteratives available on the 600 include a few of the pressure boxes ranging from VA to Ramifier. the EZ is notably absent from the list, and reading in between the lines, that means 70 HP with pressure may trip the pressure box "detector" present on that engine (the ECM senses a delta between CP3 set point and fooled pressure from the box).
However, I do agree that the VA duration box by itself runs too hot to be completely useful. It is also too strong at the low end for the stock clutch. But I don't personally think pressure is any better way to get 100HP because of the question of rail pressure. thats just my opinion from observing a few mfgs out there that are getting conservative about pressure (Edge, VA, Banks, all of which are below 24,500 psi and below 70 HP with their std products).
One dilemma we have is that 70HP pushes the limit of the stock turbocharger anyway, so you really need a different huffer to go beyond that. We should hear from guys with Quadzillas, Volumizers, and Ramifiers to see if they are able to utilize fully 100% of their 100HP boxes for sustained power in a towing situation, with stock turbos. my point is that if you're going beyond 70 HP, you could do it by stacking duration with pressure because thats better than 100HP with either pressure alone or duration alone. The VA duration/pressure stack is also easier on the stock turbocharger than the TST box is, but again you won't completely utilize all that power either without a huffer upgrade. such is life when you want to play I guess. There just isn't an optimum solution right now without injectors. Funny, Diesel Dynamics has been selling stage 2 injectors and their flavor of the EZ box for a LONG time now, and it has been proven many times over to be a very solid solution. with a huffer upgrade of course.
Attention: TDR Forum Junkies 
The Edge Juice will also have this feature if it is ever released and the VA duration box may as well, I don't know. 
