After a terrible LFR run last night, I wanted to do something new. Having never tried Proving Grounds, that sounded like an interesting thing to try. The bronze and silver healing challenges were very easy, but I couldn’t quite get gold. I felt a little better later when I read that it scaled gear. At first I thought I was failing even though I was so over-geared. I’ll have to take a look at how the scaling works later. If everything scales equally, then I definitely want more spirit. In my normal gear I cap my spirit pretty low compared to what I could have. We’ll see.
I also tried the DPS Proving Grounds as disc. Bronze was ridiculously easy, but I was about a second or two short on silver. I’m pretty confident I can do it though! Of course, I could switch to shadow too, but I want the achievement for doing it in the wrong spec.
earthwormgem
Peter (Devee)
Kor'kron 501st 
I love the Proving Grounds. They’re so much fun. Strangely, I found the DPS Gold waaaay harder than the Healer Gold, but it could just be I’m a much better healer than DPS. Still super fun.
My shadow spec is an OS that I’ve only played a handful of times even in LFR. I’m a healer at heart :)
For what it’s worth, I did the gold healer challenge as disc (pretty much 100% full Atonement with 3 or 4 emergency shields tossed out here and there) a while back without much issue, although I was running on fumes for the latter stages, I got better at preserving mana each attempt. The way the scaling works for a healer is that everything scales down equally except gems, they maintain full value… so if you want to optimize a bit, slap a bunch of Spirit gems into whatever 463+ gear has the most gem sockets regardless of iLvl. I didn’t bother, I just went in with the gear I had, figured once I hit a wall I’d make some changes and never did, got gold after half a dozen attempts, improving each time, and eventually got it. I run what’s probably a strange disc stat priority, though… Spi > Int > Crit > Haste > Mastery, so it’s possible that helped. Also, things like pots and flasks and food can help although I didn’t bother with those.
I found all 3 golds to be roughly equivalent in difficulty although I spend the vast majority of my progression time as dps so that one may be a bit harder as a result as Tal points out, I did dps and tank on my monk with the exact same gear (monk gear transference ftw), took 5 or 6 attempts as dps and maybe 8 as tank (but messed two of them up early in quite dramatic fashion so I don’t really count those).
I keep meaning to try it wrong with my priest on the dps PG, good reminder. :)
Oh, and the legendary cloak proc and legendary meta gem don’t work in PGs so to optimize, it might be worth at least swapping the meta gem (or switching to an older helm you have lying around that doesn’t have it).