The variable speed is incidental so far as i'm concerned, it'll be set and forgotten. The ac drive does have some other advantages however from what i've read in recent weeks though:

The programmable soft start the ac drive almost eliminates the additional current drawn by the motor on start up. (it would draw six times the full line current if started normally DOL or direct on line) This is important for me as i would otherwise risk popping the incoming 62A fuse on my 220V single phase supply.

Manufacturers of the ac drive (more information please visit our website: http://www.acdrive.in ) is the way to go. My friend has a metal working 3 phase band saw which he installed an ac drive. He has used it for several years and gives excellent performance.There are still a lot of 3 phase motors out there that are relatively inexpensive that can be converted to woodworking machinery without being machine specific.

A decent ac drive gives very high levels of protection in the event of overloading and so on. It also avoids the need so far as i know for an NVR (no voltage relay - drops the contacts out for safety in the event of loss of supply) in the starting switch as it contains this function by most of ac drive manufacturers.