What i'm really trying to find out is.....
will the card be able to work and transfer data to my mac via a usb 2 card reader at the full 90mbs?
downloading 16gb at slow speed isn't something I'd be willing to do and if that is the case I'd rather return the card and get 2 x 8gb non udma cards.
Short answer is no.
The speed of the download depends on the type of card reader and how it is connected.
To get the benefit from UDMA you a UDMA card reader such as the Lexar or SanDisk ones. UDMA cards can be read in normal card readers but you loose the benefit from the UDMA cards.
However, even with a UDMA reader via USB2 the fastest you will probably achieve is about 30MBs due to the real life limitations of the USB2 interface (and don't be confused about MBs and Mbs - two different speed measurements). To get faster you will need to get something that works faster than USB2; at the moment there are only 2 options AFAIK - a CF UDMA Express Card 34 reader from Lexar or Sandisk which plugs in to an Express Card slot on a laptop (if it is bus based rather than USB based) or a Lexar Firewire 800 via Firewire 800 (different connectors to Firewire 400 IIRC).
Ultimately I don't think you will get the full 90MBs at the moment but by the end of the 2011 you will probably find that a USB3 UDMA card reader will be available which will be faster still.
The main benefit of the 90MBs cards is video shooting and buffer clearance times on modern cameras. I think the 5DMKii just about falls in to this category
I have both the Lexar Pro Express Card34 reader and the Lexar Pro USB2 UDMA reader and both are noticeably faster with the UDMA cards than my old 7day shop cheapo reader. The Express Card34 is the faster of the two although it still take a while to upload 8GB 60MBs Extreme, I think mine transfers at about 40MBs rate but I have never measured the transfer.
If you want as we are probably quite close geographically I can offer a try of either, could even lend you a 8GB 60MBs Extreme as well (OK not as good as your 90MBs but you don't need to take it out of the packet first).
Personally I'd keep the 16GB card - you may not yet be able to read it as quickly as you want today, but by Christmas 2011 who knows?
