One thing I do miss is a big group and active raiding (Frostmourne is the only real alliance oceanic realm that raids) and that’s why I was thinking Barthilas for a horde but it looks like even horde are jumping ship and going to Frostmourne anyway since they have changed how PVP realms.
The only reason I was thinking of keeping my Horde on the same realm as my alliance is if I decide I hate them hordes it’s cheaper to race change back to Ally if it’s on the same server.
For the list of progression guilds in OCE: https://www.wowprogress.com/pve/oc