What will be faster when moving to sd-ext via A2SD+ Data or Dalvik-cache? (or can I move both with no extra-penalty) I'm using A2SD+ on my HTC Desire running on MIUI.
Currently only the app and app-private are under /sd-ext, but I'm running out of space very quickly :)

Currently my dalvik-cache consumes 46.3MB and the data takes 53.7MB of internal phone memory, so I think data will give me more value, but I'm not 100% sure of that either.

I know I can technically move both data and dalvik-cache to /sd-ext, but I understood there could be performance problems, but I need the space. So my question is which will have a lesser effect on performance? Moving the data or the dalvik-cache?

EDIT: Some tech info (if it helps):
My SD Card - Kingmax, Class 10, 16GB

I tested with SD Tools and got these results:
Writing Speed: 8.7 MB/s
Reading Speed: 18.6 MB/s  

Note that the test was on the FAT32 partition, I don't know if the EXT3 partition I use for the /sd-ext will be any faster. The /sd-ext partition is 1GB.
As Matthew already stated, there's no unique answer possible to your question -- all depends on your usage patterns. Generally spoken, I'd say moving app data should be preferred: If you move the Dalvik Cache, it would affect all your apps -- while moving the app data only affects apps which store some data (and by "some" I mean "data size exceeds their Dalvik-Cache size"), so a good guess is it affects only a few apps. But this can very well be those apps you are using most, and which heavily access their data -- so it may or may not be the better choice in some cases.

Guess you've got to try. I'd suggest starting with the app data. A class 10 card should provide sufficient speed -- so if the results are acceptable to you, stay with this. Otherwise, go back and try with the Dalvik Cache. If this isn't acceptable either, the only choice left is buying a new device with bigger internal storage...