I second FYRARMS decision on the Magnaflow. You had better be prepared for it to be loud. I recommend either of these places fow a universal muffler. Either www.bigexhaust.com or www.hottexhaust.com. Good Luck.
I've never heard the Borla before, but their both straight through mufflers. I imagine they will be about the same. I'm still on stock twins and it's loud enough that everyone thinks I'm trying to race them at each stoplight. Too bad your not closer to Ocala, I'm staying in Ocala for a little while.
I spoke with someone from Magnaflow and they said they didn't have an exhaust specifically made for the MKIV on the market yet, but they were still testing out their prototype. Are you looking at the general models? The biggest I found on their website was 3.5" diamter.
LLCoolJ94, I had the exhaust custom built. It took (3) 30 degree manderal bends and one piece of straight tubing to build. I just ordered the Magnaflos 4" SS (universal muffler) and had the shop weld everything up. It is pretty much straight forward and it didn't cost a fortune either.
Sorry about taking so long to get back. When I had my exhaust made, I went with mild aluminized steel. The muffler was a little over $90 shipped to my door and I had purchased my bends from http://shop.airflowonline.com . Actually the shop used (2) 45 degree bends and (1) 30 degree bend. All total with labor the exhaust about $200.00 . I imagine if you went with SS, the price will be closer to 250-300.