Well it kind of depends on the party and their gear, I can usually tell with a glance at their hp how good a group will do.
Specifically earlier today, I had a nin with 24k HP, a whm with 20kish hp, and a smn with 23k hp. I assumed they'd be fine if I pulled big and I was right, they absolutely demolished EX Gubal, we cleared the place in roughly 11 minutes. Strix was dead before he even summoned the behemoth.
