I would stick with four lights just because install is easier. I would stick with their relays and switches. I don't have the atp's but I love my 520's and I have more to mount on my basket when I get time. I've been using piaa's for 13 years and they have never let me down. Hope this helps.
_________________
RIP....04 KJ Sport
2006 Jeep Commander, 4.7L (stock for now)
Homemade Roof Rack or Thule Atlantis 2100
Comming Soon: 2.25RR", 265/70R17 Goodyear Duratracs, wheel spacers, 6000k HID's.
http://www.cardomain.com/ride/3314060