There is definitely a case for a rear bar in a race Tiger. The way a famous suspension expert explained it simply was "Everything a Tiger suspension does when it rolls is bad, so declare war on roll!"
So the first step was to stiffen up the front with much heavier springs and a bigger (1") roll bar.
Our racing experience with rear sway bars went like this (with a VERY excellent and experienced driver).
Put one on (with maximum length arms @ about 15", not the 8" Addco version). Went .2 sec per lap quicker.
Driver said go bigger. We built and installed next size bigger. Picked up another .2 sec per lap. Repeated 3 more times before driver was happy.
Backed it down one size for the Reunion races this past weekend. Driver now wants the bigger bar back.
By the way, one of the biggest drawbacks of a small rear bar with short arms is lifting the inside rear wheel off the ground. It's our racing experience that larger rear bars (coupled with the longer arms) reduce the roll enough that the inside wheel stays on the ground. (As I noted above, this all occurred after the front roll stiffness had already been increased quite a bit.)
And there seems to be no consensus in Tiger racing about the need for a rear bar. Some set up their car so the rear really sticks at the cost of excessive under steer. In our situation, the driver wants less under steer and is more than willing to deal with a looser rear. Most drivers don't have that skill level and prefer more rear stick. So there is nothing definitive about a rear bar. However I can say my driver certainly wants a rear bar and a big one at that. For him, the big rear bar is definitely faster. For others it might put them sliding into a tire barrier or wall, trunk first.
Buck,
At the beach