Hmmm, we'll see. I've found the fmsi number for both pads and i am starting to dig further. The results are that i am finding suitable pads for both calipers now. I must say i lean towards keeping the single piston calipers if it's feasible. I had single pistons on my previous car with 280mm rotors and was never wanting when i got good pads in there. And the racer i get advice from is still using single pistons on his mk5s (but they are the smaller brakes than r32 so different calipers). So i already know that for what i do, the singles will be fine.
As for the weight, you're right about the caliper weights but they both pale in comparison to the rotors. A 2 piece setup is probably a far more efficient way of lightening things up.
And again, the wheel/tire size. I did some checking and 17" hankook rs4 is $100/tire less than the 18". And i will kill a set in a season, if i am lucky.
From a $ standpoint, the best solution is the r32 brakes, if i can actually GET the appropriate pads. Though i guess the same holds true with the 18zs. As we all know these days, there is a huge difference between finding stuff on the internet and getting them into your hands.
I have flexability tho right now as i now have 2 sets of both. The passat came with the same brakes as the r32, just not painted. And they were replaced by the previous owner in an attempt to get the car thru a safety before he gave up on it.