at this point, there is very little chance that IC trucks will be the correct choice, newer (A/C controllers) electrics will have the lowest long term cost of ownership.
The only way an I/C truck can long term be more cost effective is in larger size units and/or rough terrain or on non-improved surfaces.
you might try "lift-truck-cost-tool dot com" a site Jungheinrich has set up to help make this argument.