You mention that you have used 2 versions of 10. Which 2 are they? - this will help pin point the true source of your problem. 10.0 R4 contains some very specific fixes that are not related to windows mobile performance, so I would expect the performance changes you are reporting are more symptomatic of ArcPad 10 rather than an individual service pack. (Lets not create misleading messages here).
If indeed your problems started with ArcPad 10 then what you describe is expected behavior with the hardware you are using. Remember that every application on a Windows Mobile device has a maximum memory allocation of 32MB. To start with, ArcPad 10 is simply bigger than previous versions (approximately 3MB bigger), so it will use more memory (leaving less for your project data, and subsequently a higher likelihood of insufficient memory to operate). There is also a sizable difference in the amount of memory used to start ArcPad between different versions of Windows Mobile. Windows Mobile 6.1 and 6.5 have demonstrated significantly more effective memory consumption compared to Windows Mobile 6. Windows Mobile 6 also demonstrated poor performance when loading multiple extensions. So it really is a must on Windows Mobile 6 to remove any unused extensions.
Basically somethings got to give. If you can not change your hardware, and you would like the current version of ArcPad, you must sacrifice either ArcPad Project elements (eg: use less data), or disable as much unused ArcPad functionality as possible (eg: turn off extensions).
If you would like more detail about the memory used to launch ArcPad, and its measured behavior on different operating systems, please contact Esri Tech Support. Remember ArcPad does come with Support - the kind of issues you are describing in this thread are probably better handled with Tech Support not on a forum.
