You aren't going to find the exedy information you are looking for. You can either trust me that I know better from personal experience and comparisons from Mike @ Infamous with other clutches or not. I regret the positive review I gave it. I need to get a mod to delete that shiz.
LGT stands for little girly turbo. Don't get stuck in the LGT.com syndrome of thinking a 20g is a big turbo. All you are doing by going 18g is cheating yourself out of the power you should be getting out of your investment.
The difference in lag from a 20g to an 18g is slight. The difference between either and a vf40 is more pronounced. Either way you are going to have a little less throttle response off boost.
My turbo is a lot bigger than a 20g. I don't see myself having any problems with managing lag. Look like my car is slow on a tight course to you?