You didn't say which OS .40 you have. There is a big difference between a .40 LA and a .40 FX.

If it is a .40 LA at your atlitude you will not be happy with the .40 LA and LT-40 combination. Our club uses LT-40's as trainers with an assortment of OS .40's and .46's and we are at 6000'. The .40 LA trainers fly but not well. The .40 FX trainer is passable. The trainers with the .46 FX are really the best. Stay with the LT-40 but get yourself a .46 if you can.