Onikage,
Depending upon the year of your 850, you can tweak the wastegate actuator valve to get more kick. I have done this 20-min. tweak and have felt a decent increase in speed and power. As far as manufacturers making "more power" in their chip, I would be leery about the claim. From the research I have been doing on IPD, it seems that they are building the most powerful over-all ECU upgrade on the market. Yes, some may claim more HP, but the torque curve will suffer as will the transmission as George has stated. Honestly, the easy upgrades are done once you do the exhaust, downpipe, ECU, wastegate actuator, and some other little tricks. Realistically, where do you want to be HP wise and how much work/ money do you want to spend and do? I have heard good things about Eastern Aerospace and their products. For more power, they have the real mechanical goodies there. (Things like extrude honed throttle bodies with larger butterfly valves, polished intakes, and many other goodies.) I am doing some of these mods myself at "home", and will be going to IPD once Uncle Sam returns my money via a refund check. Whatever you choose good luck with doing it.
Prospero