Diff Bush Upgrades

since there seems to be a spongy feeling in the drivetrain on/off power i thought i'd change diff bushes, though there seem to be two ways of doing it:

http://www.priracing.com/product.php/2626/183/mazda-mx5---rear---differential-mount-void-fill-bushes
buy new oem mazda bushes + the above void poly ones which comes to something like ?150
or

http://www.priracing.com/product.php/2627/183/mazda-mx5---rear---differential-mount-bushes
just replace the whole lot with poly

i would do the latter but i'm concerned about introducing more noise and vibration while trying to cure it. anyone running these?