According to boroda the only difference between 1.1.01.25200 and 1.1.00.18040 is THE VERSION NUMBER.
By the way, the easiest way to "downgrade" is actually corresponding new_opt.img file + igorsk's flasher (and then: 4 - copy, 6 - flash).
You also might want to try out this:
http://code.google.com/p/prs-plus/