Interestingly there's been threads on using Plexis for metal on the Marshall forums recently too.
As a fifty something who came from this time, I find it amusing. Firstly and most obviously, what is meant by 'metal' has changed a lot over the years. The sort of thing now meant would have been at home in an obscure subgenre back then. Second, Plexis were at the heart of a lot of 80s guitar - although usually modded, either with PPIMV or something that amounted to an extra gain stage in the preamp. Third, and core to the variac thing; it's the poweramp distortion that's really valued in Plexis and without adding variacs or power soaks of whatever kind - that means volume -and even a 50w Plexi is LOUD.
Regardless, look in the rigs of almost any period 80s metal hero and if they used Marshall you'd find some flavour of Plexi or JCM800 and a lot of outboard equipment.
I guess this is a really long way of saying 'yes, but there are easier ways...'
. JCM800s are a great starting place but even the unpopular models are crazy money now.