Upper aftermarket tubular arms are easy to justify as most should allow much more aggressive caster and camber settings without running into other issues. Lower tubulars are mostly for bling, unless you're looking at something along the lines of the SPC (
www.scandc.com) lowers which have additional features above and beyond a tubular lower that exactly matches the factory specs. IMO, Mark at SC&C is a great resource when trying to sort out all of the options, so if you haven't called him already, I would recommend it. He's also posted up the differences here and on pro-touring.com a few times, so if you do a little digging for it, you'll find it.
Tobin
KORE3