Either bike will be terrible for commuting in my opinion. But I have been enlightened by the 1000cc upright naked craze (they also makes faired versions too). Super bikes (1000) and super sports (600) are at home only on a track. They hate sitting in traffic, evidence by how fast they heat up. They are uncomfortable. They do not make any discernible power until well into their rev range, which is magnified in a super sport. They are also geared really tall. Stock gearing on the gen 5 red lines over 100mph.
For the type of riding you do, I would suggest a left over Z1000/z900 if you like Kawi. If not particular to kawi check out Suzuki GSX-S1000 (which I have), Aprilia Tuono, Ducati Monster 1200, Honda CB1000r, Yamaha FZ10. The Suzuki and Yamaha both make 160 hp. All of those bikes will be faster than a 600, more comfortable, and be more fun to ride on the street.