SFC and Watt's Linkage Questions

I have a 2002 M6 WS6 with not a whole lot done.

First, I have a conundrum with which SFC to buy. I want a quality piece, w/o breaking the bank entirely. I was eyeing up this one;

http://www.lmperformance.com/2877/1.html

That one any good? Or does anyone have some suggestions for me? I plan on road racing/autoX'ing with this car so I need to tighten 'er up.

Now onto my next question, I have heard and read some about a Watt's Linkage. Whats the benefit to a Linkage vs a panhard rod or equivalent suspension piece? What supporting mods should I have around it to get full benefits? Any advice here is also welcome!

Thanks so much to anyone who takes the time to offer me their knowledge!!!

http://www.ls1.com/forums/showthread.php?t=60459 Check that thread out.