But I think the RadeonSI hasn't implemented basic support for 290 yet, so we're still left in the dark on that one. If you search phoronix regarding the subject, you can find lots of articles mentioning it. I haven't done that though, so I might be wrong about my previous statement.
AFAIK support for Hawaii (R9 290/290X) was enabled a couple of months ago. You need a 3.14-family kernel to get the latest DPM fixes and have DPM enabled by default. What it probably doesn't have yet is much user testing since the support is pretty recent -- most of the code paths are the same as Bonaire (7790, 260X) but there could be Hawaii-specific bugs.
EDIT - just checked mesa logs, looks like most of the Hawaii-specific activity in radeonsi was in the last couple of weeks of November.