If you really want more hp go buy a 550i.
As far as these two cars, the 08 has rear side airbags(important if you carry passenger or children), the Sport Auto with paddle shifters which is fun to have, sunshades(nice for passengers again,), HUD (which is nice but not necessary) and the clincher for me is the LOGIC7. I wouldn't consider any car without an upgraded LOGIC7 system. I love the PDC but it can be added(I believe) easier and cheaper than a LOGIC7.
For either car ask for the Y-adapter cable for the iPod & USB.
My vote is the 08; more options, less mileage and money.
Is the 09 also black?, stone chips?, CarFax?. Was the fleet car driven by one person? Test drive both. Every car drives differently. 08 price seems high but not outrageous. Negotiate, negotiate. Definitely get an extended warranty in deal.
2012 BMW 535i X-drive; Space Grey/Black Dakota, Fineline; Executive (Auto trunk, NAV, HiFi Prof, Lumbar, Rear Cam, SIRIUS, Voice), Technology (Blind Spot, Hi-Beam Assist, Lane Departure, Surround View), APPS, Rear heated seats, Tint.
Retired: 78 300D, 81 300SD, 87 190E, 88 Porsche 924, 89 260E, 93 300E, 97 Volvo 850, 98 E320, 03 BMW 325iT, 02 C230 Sport Coupe, 08 BMW 535i