'3' 100M to 20-30M wifi

Dear Si Hing,
I just upgrade my '3' broadband from 30M to 100M.  I found that when using fixed line, the max speed is only around 60-70M and when using wifi router, the signal drops to around 20M. Is it normal or it is other problem, i.e.  the power of my wifi router? I am now using Netgear WNR2000 router, which is only a rectangular box with all antennae being hided. It is so frustrating! If so why I need to upgrade!!!