Michael at Eurotubes got back to me on the higher gain pre-amp tubes:

The high gain ECC83S's have about 10-15% more gain than standards which adds a bit of bite and a sharper dynamic but does not hurt the clean tone. The other attribute that these tubes have is a faster filament rise time which is great for an EVH type style and is also good for fast palm mute and metal styles. They certainly won't replace an od/distortion pedal but if you're looking to coax a bit more gain and attitude from the overdrive channel then they are a good way to go. They don't really breakup faster than the standard ECC83S's, they just have more gain on tap. Imagine if your gain knob went to 11 or 12 instead of 10...
Sounds like it could be a good option, although as you pointed out, Tung, I'm not sure how the rest of the circuit is set up.