What class MicroSD card?

Check here:

http://www.poi-factory.com/node/39227

All my good experiences have been with Sandisk.

All my not as good experiences have been with other brands.

2gb its fine

2gb its fine

2gb its fine

I do not believe that the GPS writes to the card. Since write only happens once when you copy a mapset to the card, read speed is what you really care about.
Over the years I've acquired a number of cards from various manufacturers for different purposes and tested the cards. (Read & Write are in mb/sec) Below are the results:
The chart is difficult to read because I haven't been able to attach it in table form. Of the last two numbers, the first is write speed and the second is read.
4 gb Sandisk Class 6 15.60 18.40
32 gb Transcend Class 10 15.90 18.40
4 gb Sandisk Class 2 5.24 18.30
32 gb Sandisk Class 4 4.21 18.30
4 gb Kingston Class 4 10.20 18.30
16 gb Sandisk Class 4 4.43 18.30
8 gb Transcend Class 6 9.88 18.30
4 gb Sandisk Class 2 5.50 18.00
4 gb Sandisk Class 6 11.60 15.10
4 gb Transcend Class 4 10.70 14.90
4 gb Sandisk Class 2 4.54 10.10
4 gb Sandisk Class 4 4.95 10.00

Interpret the results as you wish. The two lower performing cards may be very old or counterfeits.

It's interesting that some of the Class 4 cards outperform some of the Class 6 cards, even the same brand. Did you try running any of those tests more than once to see if the results were repeatable?

I always did like the Kingston cards, I've had very good luck with them. I tried some off brand SD card once (I think it was a Viking, actually) and it actually screwed up the card-reader I had.

- Phil

The nook color ereader sold by Barnes and Noble can be converted to run the full-fledged Android operating system and the Android OS can be installed to the internal nook color or can be run from a SD card which leaves the original B&N OS inside the device.

Most of the gurus who created and users who use this CM7 and now CM10 OS on nook color devices being run from the SD card strongly recommend using only Sandisk Class 4 SD cards since some other brands and even faster Class Sandisk SD cards may not work as well as the Class 4 Sandisk.

Running an alternate OS from a SD card will involve both writing to and reading from the SD card which should challenge the card more than using one to store maps on a nuvi where the card is only read and not written to.

Just my 2 cents and I'll stop now since I doubt I'll be able to offer more than the above. Since my supply of SD cards tends to be Sandisk Class 4, that's what I use in my nuvis (for the current and past City Navigator on my 750 and for the large JCV file on my 855) and they work well. I'm not sure that paying more for a faster SD card will offer much to nuvi users.