I now do all my RAW processing in Lightroom, but CS6 camera RAW got a pile of great upgrades to highlight recovery, shadow lightening, automatic CA processing (along with LR 4). Styles on groups has potential to be very useful (i.e. something in the past I've wished they had) but in practice, having lived without it for so long, I've never actually used it in CS6

I don't find any of the new content aware stuff very useful in practice - there are enough flaws in what it does that you have to fix things to clean up after it. And if you're good and fast at doing that, then doing it yourself in the first place is faster. The healing brush is great for sensor spots, but that's several versions ago.
I'd still recommend you get CS6 to extend the period you can use a "perpetual license" as long as possible. As OS upgrades come, sooner or later one of them will break something in Photoshop. More likely to break CS5 sooner than CS6 as the former is older.