Interesting update. Received my Voltaire ISR9024D-M this week. It came with firmware version 0.8.6 on it, and all of the ConnectX cards (MHGH28-XTC) were reporting as SDR speeds for every connected port.
Upgrading to firmware v 1.0.0 didn't change anything (still SDR speeds), but after the upgrade to firmware version 1.0.5, all of the ports are being correctly reported as DDR speed now.
Side note - the ISR9024D-M doesn't seem to run silently. The fan module can be removed, but the temp rises too much to leave it that way for more than about 10 mins. (even with the subnet manager turned off)
I'm guessing the 9024D can be run fanless, but the 9024D-M can't be. Oh well, it's not killer loud. Better than the Cisco/Topspin switch I used to have.