I promised to take some size comparison photos when I had a chance. Not the best quality but here they are.
From my necromancer/skeleton warband.
From left to right: Frostgrave soldier with GW head, Wargames Factory viking body with frostgrave arms/crossbow and GW head, Reaper Bones, GW, Reaper Bones, Frostgrave soldier with GW head.
Some random historical and fantasy minis.
From left to right: Frostgrave soldier with GW Mordheim head, Gripping Beast viking body and arms with Frostgrave head, Frostgrave, Gripping Beast russian, older GW Empire, GW Mordheim, Reaper Bones Anhurian.
Hope this helps and if there's any other comparisons you want to see I have a ton of older GW minis, a lot of the Reaper Bones, Frostgrave and some different historicals.