I've read the manuals and scanned the posted messages, but I don't find an answer to my question:  How long should the takeoff roll be with 50% fuel load, full passenger and cargo load with GTOW of about 250,000 lbs?   Departing from KSEA on the 8500' runway, night time, ambient temp about 40 degrees, wind calm: I used second notch of flaps, set 2 of the 3 turbo switches to START, shut off all 4 bleeds, opened the L and R wing valves.  I held the brakes on while bringing up the power to around 65%, released brakes--and rolled forever while gaining speed.  I rotated at about 7500 feet but didn't unstick until after 8,000 and just barely cleared the approach lights.  I didn't get a good rate of climb for probably 2 or 3 miles from the departure end.  I know the 707 doesn't have nearly the performance of the 737, 757  etc., but should my take off roll have been that long?  Am I missing some steps in the proceedures?

Yesterdady I dug into the aircraft.config file and found what I believe may be the relevant entries affecting takeoff power.  In the engine section, there is a rated N2 rpm of 10095 and static thrust of 18963.  I queried online the specs for the JT3D-7 engines and found this item:

http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/4f009e533a1...

For this engine it lists a rated N2 rpm of 10300 and static thrust of 19285. 

Before I had these specs I experimented with changes to the rpm and thrust settings but even with small changs to either of these settings crazy things happened affecting the airport graphics and the 707 actually took off backwards with the throttles at idle and the parking brakes set. 

Should the rpm and thrust in the config file be set to the higher values, and if so, what else must be changed in the config file to avoid screwing up the graphics and performance?