Older versions are not likely to run any faster. If anything, speed and satiability will get worse as you go back to older versions.
CS5 and CS6 may run a little faster because it can take advantage of 64bit instructions. The DCT transform of DV is an example of such code that would benefit from 64 vs 32 bit instructions.
eg: x264pro got 50% faster when it went from 32 to 64bit.
I'd like to see a comparison with say CS2. I tend think that your current software might run marginally faster. I warn you against going to CS6, as it seems to have higher computing overhead thus far, and there has been some issue with DV editors connecting to dv devices. I don't see where it could help your dv workflow very much.
But Dude.....,Pentium D, 3.60GHz? You could build a new PC funded solely by the electricity that you would save over 18 months. Combine that with savings from not upgrading to CS6 and join us all here in modern computing land. Editing HD natively (It will happen for you) without rendering previews, exporting to DVD and mp4 in minutes instead of hours. It is so worth it. Is this your work's or your church's system where its just not your choice to upgrade? Here at work we were finally able to upgrade to CS5 capable systems 2 years ago, and HD material had already become a big workflow issue with us, even though we were primarily working with DV. I also had to upgrade my home system to take on any freelance editing. You can rock with any modern i5 or i7 quad core, 12gb memory, and a gtx card. You could also get and AMD 6 or 8 core and maybe save a little $ there.
I just wouldn't ever consider upgrading the software before that rig.
hahahaha, yeah, you are right. I am in the planning of upgradeing my system. Is just that since I was working only with DV it was working fine, and the system even though old, it work great for this and other stuff. Anyway the question is valid, since I can assign this system to another person that might work easy stuff like cut editing for example, and I was curious as if for an older system you should install an old version of Premiere for better performance based on the fact that CS5 works fine. Thanks for your advice in not getting CS6 mainly for DV. I know on the newer system will be great for HD.
Also thanks for the other responses that states that newer versions should work better.