Pffff.... we are trained to stop our breath for at least 15 minutes while rescuing our buddies using only one hand and taking pictures of the surrounding environment for documentation purposes!
Now, according to my basic understanding of GUE system (I am not an instructor nor an experienced explorer!), the principle of this emergency ascent is that, if everything goes as GUE want, in an OOA scenario the OOA diver ascends using the buddy's gas, and the gas is calculated so as to allow a safe ascent at that speed.
That said, one has to use the brain. I had to share gas only once*** in my life because of a free flow regulator, it was a stressful experience, but we were three, with plenty of gas, and the situation was manageable. So we ascended respecting the standard ascent speed. But in a different, hard-to-manage situation, maybe in a team of only two and very far from any deco issue - no way that I am going to ascend that slowly. It all depends on the situation, and the priority is to survive, always.
The point is that GUE approach is meant to avoid these hard-to-manage scenarios, but if (
when) **** happens - use the brain
***I actually shared gas another time, but it was just to prevent a possibly bad situation, so not really an emergency