TBH, looking at the specs/prices these integrated products are very compromised
I would heavily suggest you consider a 'proper' PDA, and then look at the GPS Options
For instance the DELL X51V is a proper PDA
1. VGA Screen - 4 times the resolution of all these integrated devices, much better for web surfing and video playback
2. 624Mhz Intel processor
3. Compact Flash (CF) and SD memory slots, you can have 2 memory cards at once, for example, one for SAT NAV Maps, one for Music/Video/Data.
4. Bluetooth and WiFi
5. Accelerated Graphics Chip - more video players/games are starting to support these.
6. Very nice form factor - not compromised with the Bulky GPS aerial etc.
7. being popular, cases/accesories/support are all easily available
This PDA Is available for around £240 when on offer.
Then looking at the GPS Options
CF - this closely follows your 'integrated' ethos, these just pop in the CF slot on the top of the device, and depending on the CF card you get, you can have flip out aerials, stub aerials, etc the choice is yours, this still leaves the SD card slot free for a memory card, this gives you an all in one top notch PDA with the BT/WiFi/SD Card slot, etc.. CF GPS cards with SIRFIII can be had for £40+ on ebay. being technically seperate, you can then upgrade when/as you like without being forced to upgrade the whole PDA.
BlueTooth - A Small device, self powered, can be put anywhere within 10M of the PDA, which occasionally is handy. Being seperate, can be upgraded without having to buy a new PDA. can be used with Smartphones/PC's etc, or anything that has bluetooth and Navigation software
It seems that for the same price you can have one of these 'compromised' all in one Asus PDA's, or a top of the range PDA with CF GPS