…for me, it’s not a question.
In Patch 4.0.1, Blizzard made 310% riding speed purchasable, rather than tied to specific mounts. If you previously acquired a 310 mount (such as one of the achievement mounts from Ulduar or ICC, or from the holiday meta-achievement) you upgrade to 310 automatically upon mounting the first time after downloading the patch. If you don;t have one of those mounts, you can now purchase 310.
But the price is steep: 5,000 gold.
This is a pretty obvious gold sink, much as the original epic flying speed (280%) was a big gold sink in BC and through most of Wrath, going for that same 5,000 gold. But the benefit of upgrading from the basic flying speed (200%) to epic flying at 280% was substantial. A nearly 50% boost in speed got you places noticeably faster.
The upgrade to 310% is no where near as impressive. A boost of 30 percentage points sounds like a lot, but in reality, it’s a net speed boost of just over 10%. If you’re flying from one end of a continent to another (say from Valgarde in Howling Fjord to Coldarra in Borean Tundra), the difference might be noticeable. But how often do you fly that far at once? And certainly, there are faster ways of making that trip than flying directly, such as hearthing to Dalaran and flying from there. For the most part, when you fly, it is within a zone, or to an adjacent zone, and that 10% boost in speed is not nearly as important.
I have a couple of toons that got the 310 riding by virtue of obtaining a 310 mount prior to the patch. For the rest, I’ll be fine flying along at 280%. The additional 10% boost in speed just isn’t worth 5,000 gold. I’m sure I’ll find better gold sinks in Cata.