I installed the Perrin transmission support replacement part yesterday on my FR-S:
It had the effect of immediately stiffening up the drive train. Previously, I had noticed a slight twisting of the transmission case (through the shifter of course) and a corresponding wiggle from the tail of the car. That is completely gone now. It launches very straight and the feel of the car is very solid and crisp when shifting. The part is inexpensive ($50) but it will take 1-2 hours to install and you will need to have access to a lift.
There is a noticeable increase in gear whine from the transmission in 1st-4th gears, due to the more solid connection between the tranny case and the transmission mount cross member but I did not find it annoying; in fact I rather liked it. Highly recommended if you don't mind the additional noise.