I was finishing up the purple belt quest so I could do the Brown Belt quest earlier today, killing Tremor Rams as they popped. I'd been doing it on and off for 2 days without much luck. The Tremor Ram spawn time is exactly 10 minutes from the last death, by the way, not 12 as you may have heard. I'm told that 2 Rams spawn at once, but I never actually saw a second one.
Anyway, the next spawn time arrived, I hit wide scan, and sure enough - there's freakin' Steelfleece Baldarich, the rare spawn of the rare spawn of the rams I was hunting. The worst part was that, being level 60, killing this guy wasn't out of the question for me - but my linkshell was almost completely devoid of life at the time. Unable to put together a party to kill him, all I could do was follow him around and poke him until I gave up, warped to Jeuno, and shouted that Steelfleece was spawned. Once a group had killed it, I returned to my camp.
Now here's the interesting thing. I'd planned to take a break for a while, since the Rampaging Ram surely wasn't going to spawn for a while after this. But, having nothing to do, I kept at it. And amazingly, just 30 minutes after Steelfleece's death (or 3 spawn cycles), Rampaging Ram appeared. I killed it quickly and was on my way.
I think that's a helpful bit of information: Rampaging Ram and Steelfleece Baldarich can spawn very shortly after one another. This might also mean that RR can spawn twice within a short period of time, but I don't know that for sure.