Coolxap.com indicates that when an SD card in inserted into a phone the system will automatically turn off the ability to run apps from the SD card (i.e. it will not appear as an option in the Settings app). The site also indicates that Class 6 SDHC is the minimum level of support and the for optimum performance a Class 10 SDHC card is recommended. This means Class 2 and Class 4 cards will not be supported for running apps, though theoretically should be usable for storing content.
The majority on microSD cards on sale today are Class 6, with premium products generally being Class 10, and budget products Class 4. There are six commonly used performance classification used on microSD cards currently being sold:
- Class 2 - minimum performance of 2 MB/s
- Class 4 - minimum performance of 4 MB/s
- Class 6 - minimum performance of 6 MB/s
- Class 10 - minimum performance of 10 MB/s
- U1 - minimum performance of 10 MB/s
- U3 - minimum performance of 30 MB/s
A card equivalent to the SanDisk Ultra 32GB Class 10 microSD card is going to give good performance on Windows Phone. A higher performance microSD card is also useful if you regularly record 1080p video (Class 4 theoretically "good enough", but Class 6 or 10 recommended) due to performance required to writer a video file to the card.
The same report also provided confirmation for the idea that the three column wide Live Tile start screen, as seen in the Lumia 1520, 1320, and Icon, will be available as an option for any device with a screen over 4.5 inches in physical size. For Nokia devices, this would mean the Lumia 625, 920, 925, 928, and 1020 would all get the option. The Lumia 520, 521, 525, 620, 720, 810, 820, and 822 would be excluded.
Image credit: @tomwarren