Well, I did what you suggested and this is what I came up with. I chose 2 random players (1 Hitter and 1 Pitcher), compiled their numbers from 20 random PB teams, averaged them and compared to their corresponding ML season. The results were:

Brad Wilkerson (PB) 15HR .238 AVE .397 SLG .347 OBP
Brad Wilkerson (ML) 19HR .268 AVE .464 SLG .380 OBP

Mark Prior (PB) 213 IP 18 HR 52 BB 253 SO 2.92 ERA
Mark Prior (ML) 211 IP 15 HR 50 BB 245 SO 2.43 ERA

What that shows me is that for hitters it appears that their numbers across the board will be lower from 9% to 14% for almost all categories with the biggest differences being in the power columns of HR and SLG. For pitchers however, the numbers are almost identical except for HR and ERA which are both up about 20%. It would be interesting to see if these same ratios would hold up for different caliber of players, but the above might be an indication of what to expect from PB in regards to stats comparison. Any comments?