The one issue with scale is that of the HT parts I have (and I have a lot) is that many of the parts - including the helmet feel about 10% oversized due to the fact they were designed to go on a finished figure that approaches 14". I think that's what is giving the ESB Vader that "dumpy" look a few people have mentioned - that they put the slightly oversized parts on a smaller body and it starts to take on that "teen wearing adult clothes" thing.
Those two look epic together.
It does show how Vader (in all HT variations) overall is just a wee bit enlarged and overscale. Look at the size of his helmet.
I think both of you are 100% correct about the HT helmets being oversized. All of them so far. And I think the helmet is the reason that the rest of the costume parts end up looking wrong on these figures. But, the good news is that I think the other parts (body included) are scaled pretty well. It's just the helmet sizes that have been ridiculous; and I think I can illustrate it conclusively. Just please be patient with me here because I have to explain it in steps.
First, here's a photo of HT ANHv1 Vader body, helmet, undersuit, & boots - with v2 shoulder armor. I added the new ESB vest (w/ chest box) because I want to scale things to ESB since this is an ESB Vader thread. Everything might seem properly scaled/proportioned (but the helmet is far from it).
I took the same figure, but swapped helmets with a broken Sideshow ESB/ROTJ one (not the Deluxe version). Here are the two photos cropped next to each other. Aside from the hideously terrible sculpt on the SS mask, you might think that the dome is way too small. It isn't; the mask is just too big. Stay with me here.
Now I'm putting both version on either side of a shot from ESB movie Vader. I drew some yellow lines on it to get a sense for the size of the shoulder armor and chest box. The green lines are for the body scale (using body width just under the shoulder bells). I slid all of the lines to both the HT helmet pic and the SS helmet pic. You can see that the body width, chest box, and shoulder armor are very closely scaled with the movie image (though the shoulder armor is shaped horribly). But look at the helmet size! In particular look at the domes!
The HT one is just absurd. The SS dome, however, actually comes pretty close in terms of size/width; but the mask inside of it is way too big.
The helmet is the problem. Just too big. I think the v1/v2/ESB body is scaled reasonably accurately. I think the other costume pieces are scaled pretty well. But the helmets are so big that the height of the figure ends up being too tall, and the whole costume just ends up looking off because the helmet is the key feature. Everything kinda flows down from the helmet.
In my opinion, HT would have been better off scaling their helmets closer to the size of their Luke-face helmet from the DX07 Deluxe set.
How's THAT for some tedious Vaderology?
Sorry for all the detail and over-explanation. I just really wanted to try to settle the debate about scale/proportions. For the most part, I think everything is okay on these figures except the helmets. The rest can be futzed or padded well enough to get very close to screen accurate, imo.