Assuming that USB drives will appear always in that order, the entry you propose is correct. Go on and try it out
You could also try Old-Polack's advice and have two entries in your menu.lst in case your Knoppix USB drive is seen before the Readyboost one.
Question 1: why do you use FAT32 on the Knoppix disk and not a Linux filesystem (such as ext3 or ext4)?
Question 2: does Readyboost really make any difference in Windows?
Question No. 1: It is a good question for me. I should have formatted the Pendrive in ext4. I simply leaved the FAT32 that it has.
Question No. 2: I really do not appreciate much change in Windows performance, although my system is new and I just used it for a couple of weeks without ReadyBoost, and now, with it installed, I only have 3 weeks. My physical RAM is 8 GB, and the ReadyBoost Pendrive is 4 GB. What I do notice is that Windows seems to use the Pendrive a lot, since the little light of it flashes very often.
Tonight I will do the change in /boot/grub/menu.lst and will post.