I have same problem. The 403 page consume about 300GB per day from my server bandwidth. The problem is i can't block attackter IP because he use more than 5000 bots and how i can block them ???
Also LS don't support DROP in mod_security, which apache support. I think you sould think about it.
No one of optimized ddos settings help me, my server receive 14000 Re/Sec (70Mb/s) attack and litespeed only can limit proces by the user. I think if only Drop work,everything gose ok.