I thought someone had tried to start one of these before, but after browsing 10 pages deep I wasn't able to find it. That said, let's get a nice list of what we can solo post-ROI. With the level of DPS we can put out along with some of the awesome set bonuses we get, Captains are capable of amazing things now. I'll start with my couple minor achievements.

Grand Stair Hard Mode
Stoneheight T1

I had done Stoneheight T2 through the first boss, pretty sure boss 2 would be easy as well, but ran out of time and haven't been back since. The last boss/challenge for StH T2 would be pretty difficult with all of the stuns and massive hits the one guy throws out.