In this discussion there needs to be a reference point for an extreme grip hitting "way out in front."
Way out front compared to what? A 2hbh? Conventional wisdom says yes.
But this thread is about comparing a conventional 1hbh vs. an extreme 1hbh.
Therefore, we should compare the contact points of two these types of 1hbhs.
As it turns out, a switch from Eastern to Extreme Eastern (moving both knuckle and heel pad back by 0.5 bevels) will probably move the contact point by about 2 inches. Not much at all.
In fact, a bigger change is going from "steak knife" Eastern to a "modern" Eastern, which adds about 4-5 inches to the contact point. That's a significant difference, so this deserves some thought.
A "steak knife" has more lateral reach, is easier to flick, and can be easily hit without having to open the shoulders. Combined with a willingness to slice most balls above belly, this stroke can be part of a comfortable tennis style. It might be a reasonable choice for some casual players, older players or someone with a really good slice, etc.
Unfortunately, the steak knife Eastern is not good for even moderately high balls. So if a "steak knifer" wants to drive most his backhands, that means either:
1. He has to hit OTR consistently, which is tough to do; or
2. He has to constantly back up on medium-high balls (or stay back) and/or hit more defensive shots, which is ultimately more physically demanding than hitting with a modern grip from good position.
So in short, using a slightly stronger grip (whether we're talking knuckle or heel pad) shouldn't typically add that much overall physical demand, especially if he/she is already trying to slug it out from the baseline. And it may actually save work.
However, I could see how a big jump from, say, a Federer stoke to a Mauresmo stroke would probably add more work.