chnco - No one has had a 57 in long enough to really tweak the sucker. We're working on it, though!
My car (SP57 on stock fuel) dyno'd consistently around 475-480RWHP at 17.5PSI with fuel problems (ECU kept wanting to go lean) without a fuel controller. After putting in a GCC, it feels a lot smoother on the big end now, and hopefully is a little more dialed in - will try to get back to the dyno soon. At 18PSI, I've twice run down the 1/4 bouncing off the limiter in 4th right before and all the way through the traps (124.53 and 124.55MPH). At ~15PSI, the car dyno'd 448RWHP/433RWTQ with good A/F's.
Dyno sheets from some of the 17.5PSI runs with fuel problems can be seen at
http://pete.waterman.net/single/18PSIdyno.jpg - pictures of the install and some old timeslips at
http://pete.waterman.net/single.
It has a LOT more in it, on the dyno it didn't make boost as fast as on the street under more load, and one run with more boost (~24PSI) showed ~410RWHP/~530RWTQ by 4200RPM before letting off (going too lean without that fuel controller).
In theory, the SP60 will probably make 2-5RWHP more depending on boost, and spool a little slower. At higher boost (20+PSI) it will probably make this gap a fair amount larger. It probably spools a couple hundred RPM slower. (they both have the same size compressor wheel, but the 57 has a smaller exhaust wheel)
For more info on the 57, do a quick search in the General Forum for my thread titled "SP57 First Impressions" - more details than you can shake a stick at.
-Pete