MobiNav

The GoPal X4510 gets a larger 4″ display screen. It uses a gyroscope and an electronic compass in order to simulate navigation with noGPS reception. It also has a micro SD port for removable memory. Key features include a 4″ display, 324MHz Centrality Atlas II Processor, 256 MB internal memory MicroSD port, Hands free Bluetooth, Integrated RDS/TMC Receiver available in premium versions, GoPal 3 software, MP3 playback, a photo viewer, Remote control for steering wheel, and Windows CE 5.0 The retail price of the GoPal X4510 is expected to be around 499€.

look here

Speed issues:

The read/write speed is dictated by the microcontroller speed on the SD card itself.  Here is a good explanation of SD Cards

Can’t be stated for sure. With cheaper card, FAT16; with some high-end ones,
FAT32. Read http://pocketpcmag.com/forum/topic.asp?TOPIC_ID=17921 , it
explains everything.
Esentially the fewer clusters of the card, the faster it will read and write.

Fat16 vs. Fat32 performance tests http://www.geocities.com/SiliconValley/Peaks/9892/fat16vs.htm