I personally like the idea of a panhard rod, if not for only lowering the rear roll center a bit. Although that would only be an issue if you had changed the front roll center. Unfortunately it's all theoretical as i don't have a race car.
People are split on whether it is worth it or not i would say there are just as many people for and against a panhard so i guess it comes down to you.
it's been said if you have a number of locating holes in your panhard brackets so you can set up your panhard at different heights then you can adjust your rear roll center.
If i had a race car i would want all the adjustability i could have so by using the above you have another degree of adjustment
could be worth investigating some more.

Nick

I raced a 1200 coupe for a year and a half. There were two other people also racing coupes at the same time as me, both with different powerplants. I had a hot 1200, one had a very hot 1400 and the other ran a 4age. All of us ran uprated rear springs and good shocks, nothing more. Im now putting a hot 4agze into my two door sedan and Ive been looking around for trick rear suspention to get the power to the ground and very few (infact almost no one) seem to be running panhard rods, anti tramp bars, swaybars or any other links. WHY? is it just because the cars so light it doesnt need much controling? Or are there only a few people who see the importance of a well located rear end?