Groovemaster, what you are feeling is reduced flex in your mounts and as a result engine does not have to move before power reaches yours wheel, I experienced the same when I went to poly mounts front rear and gearbox mount, driver side is still oem but filled.
As for only filling one mount, it can make a difference, but it will reduce the life of the rear mount. If I were you I will fill both the front and rear. From research the msp front mount is a bit stiffer so you can look at that. http://www.protegefaq.net/mods_engine.html#mounts http://www.mazdas247.com/forum/showthre ... ine-damper