My 6mm stuff is mainly H&R, NavWar and Scotia.
GHQ is fine but much bigger than 1/300th, same for Adler (don’t like the big heads) and Baccus have pretty much redefined 6mm as something more akin to 8mm.
Much of my non WW2 6mm is Irregular. The sculpts do indeed look awful in the raw lead, but paint up very well indeed. They also have a large range of 2mm, which I use for a number of periods including Cold War.
People seem to really like the 1/600th Pico Armour stuff, and maybe if I was starting again….
"Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke