It's possible that the HP might not have as good of memory handling as the Casio. I found that the biggest resource hog on the HP is the Media Player. Trying to run other programs while this app is running is really a lesson in frustration due to the overall slowdown. Of all three Pocket PCs, the HP does feel the most sluggish. I would also have to say that after having used an iPAQ, the HP feels really slow.
Battery life appears to be pretty good.
The batteries are supposed to yield 8hrs of use from one charge. Since usage is hard to track, I did do a little test. Starting with a fully charged battery. Charging the batteries seems to take longer than with the Casio and iPAQ although this may just be my imagination. On to the software side of things.