well you know my thoughts and that I have the progress springs. If you want more of a lowered look than mine, the intrax would probably be the next step. This is also the cheaper way to go. If you want to spend the money, buying matched set of springs/dampers would really be nice. not sure about brands though. Remember, the stiffer you go with just springs the faster you will have to replace your stock dampers and the "harsher" ride it will be.
your best bet is to search in here and really the suspension forum. There is loads of info there. Search specifically for the svt and type/brand of spring/damper. And prepare to stay up late reading!