I ended up paying extra for a class 10 card. The articles i read claimed that class 6 ought to be good enough, but there seems to be a dearth of class 6 cards on Amazon, at least b well known manufacturers. There are a lot of class 4 cards and a number of class 10 card, but not a lot inbetween.
So things i've noticed, my phone seems to be a _lot_ faster and more responsive. There are a lot of possible reasons for that.
The class 10 card instead of what i had before. The fact that it's a new card without any bad sectors. The fact that i haven't loaded any of the apps to the SD card yet. The fact that i cleared out the onboard memory and reinstalled the OS, possibly any cumulative slowdowns there. (Everyone knows that OSes get slower over time, even though there isn't always a clear logical reason for it.)
Interestingly, even though i think i've reinstalled all the big apps i used to have, i still have 44 MB of main memory free, as opposed to the 18 or so from right before the reboot, despite not having moved any of the apps to the SD card yet. Either i had a lot of miscellaneous space taken up by smaller apps, i'm missing one or more big apps and just haven't noticed it yet, or the cache for some of the apps had built up to a rather large size. I'm kinda suspecting the last one at the moment. I seem to remember both Maps and Browser ranking a lot higher in the size-sorted list than they do now. Getting those apps to let go of their cache was always a hassle, especially for the Browser since i wasn't sure how to dump the cache without also forgetting remembered passwords and such.
I've also noticed some stuff that's gone missing. I backed up all the really important things, and i still have the old semi-readable SD card for reference, but there are a few things that were apparently stored only in the internal memory. Most notable it seems like all my playlists are gone beyond recovery, so i'll need to spend some time recreating those =P
In other news, i did end up grabbing the Farscape boxed set while it was on sale. And as long as i was looking around at stuff on Amazon, i also ended up adding Princess Tutu and Romeo x Juliet to the order. Of course if Amazon ends up having another anime sale anytime soon like they did a couple years ago i'll feel pretty silly about having done that :)
I'm grabbing Princess Tutu because there's an awesome AMV set to it, and the first episode on Netflix seemed decent, except for being dubbed (which is why i'm not continuing to watch it on Netflix.) Romeo x Juliet is entirely on spec, because it also has an awesome AMV set to it and it was only $16.