Crank Bolt Torque?

[!TREK4ME!]

I just need a little clarification on the torque specs in the Parks repair manual. In the torque specifications for Shimano crank bolts they give a broad range of torque values(305 inch pds - 390 inch pds).
-How do you know what to tighten the bolt to??
-Should you go to the lowest, middle or the highest torque value??
-If the cranks don't get tight enough, you can end up with a wallered out crank that will never stay tight, right??
-If you go too tight you might split the crank, right??

Sorry for all the ??'s

[!TREK4ME!]

Thanks painkiller.
The reason I ask is I torqued a new crankset to the middle value and the cranks kept loosening up after every ride. After the first ride and discovering the loosening, I cleaned up the bolt and threads and then applied blue locktite, then torqued to middle value again. I let the locktite cure for the recommended time and then went for an average ride(15-25 miles). They loosened again. I then repeated the same procedure, but with a little tighter torque and a 2x recommended threadlock cure time(2 days). They loosened again after an average ride again !!
After this, I tried again with the max torque and let the locktite dry for 4 days. I did another average ride and they loosened again !!!
What is the deal ???
This was a brand new crankset on a roadbike with low to medium crank power being used. I have'nt even stood up on the pedals to really crank down on them yet !!
Not sure if it matters, but this set uses a 8mm hex head bolt instead of the normal 14mm bolt. Does this matter??
Thanks

[cny-man]

If you replaced the cranks but not the spindle you may have mixed two incompatible tapers - JIS and ISO. the BB. http://sheldonbrown.com/bbtaper.html. If that is the case and you are lucky you may be able to keep them tight once you have replaced. If not you unfortunately are possibly out of luck.

Otherwise I would have no easy explanation, as the middle range of torque should be sufficient - we went decades wrenching on square taper BB's and no torque wrenches without a problem.
The crank bolt type does not matter.