I have a GT top triple and risers on my S1K and I use a Renthal alloy bar. I like them. They are well made, the heavy wall construction doesn't vibrate like steel bars, they're reasonably priced and several height/bend options are available. I think the Rizoma's only come in one height/bend. Since the Renthals are 7/8" they bolt right up with the stock risers. I would have liked a tapered bar but I thought the $100 asking price for risers was rather steep and you also have to modify the Rizoma risers or the GT top triple to install them so I just kept the stock risers and used the 7/8" bars.
I have the road ultra low bars on the S1K and they are located in almost exactly in the same place as the higher clip-ons that '07 S1K's came with but are much taller and ergonomically more comfortable than the low clip-ons my '06 monoposto came with. I have the Renthal road low bars on my bevel Duc which are a bit taller and I am thinking about swapping them onto the S1K to get slightly more height since it's a long stretch over the tank to the bars especially around town.