From what I've seen the lag fix does nothing too noticeable.
I had it installed (Ryans OCLF) for a bit, then decided it made absolutely no difference and uninstalled.
For what it's worth, I've seen many people complaining or begging for help after installing the lag fix (unsure if they had Ryan's or a different one) that, combined with it's questionable effects, I would never really recommend it to anyone.
Obviously it's your phone, so do what you want, but I'm not bothering.
After getting a fresh start (exchanged fascinate for another), I'm giving touchwiz a chance, and not rooting the phone for a month or so. There's really not that much out for the phone anyway, so I'm in rush.