The range is used because of all the variables involved, (friction on there threads, under the bolt /nut head, stretch of the bolt/stud etc.)
By using the lower end of the range wont "free up" the engine and allow it to spin easier? That is caused by the bearing clearances, A lot of old school builders used to run loose clearances for this purpose and to allow more oil flow which helps bearing cooling.
The best way to accurately measure the correct tension is by bolt "stretch" but the Torque method is usually used, but some FSM's now use the No. Of Degrees of twist on a Angle torque wrench check these links.
http://www.ferret.com.au/articles/cf/0c0203cf.asp
http://news.thomasnet.com/fullstory/484855/2196
I have ALWAYS used the higher limit when I assemble an engine. using a regular type Torque wrench
Also if "race engine builder assured me" uses lower torque settings to build loose "race" engines I would go somewhere else!! (just my 2 cents worth):confused: