I have a couple of questions:

Do/will you have bottom beams ( Ie first pallets off the ground)

what goods are you handling ( ie heavy/light, are they well packed or neat pallets.

As the above mentions, Crown/Raymond do a good pantograph truck which I have seen in a 2900mm aisle, and thats no mucking around room for error sort of stuff. Bottom beams will ad a cost to your rack but will allow for straddle legs (depending on the model you choose) to go under the rack, which will enable an easier (yet Illegal) drive with the load straight into the rack. To be comfortable and without compromising productivity an ailse of at least 3200mm would be nice. Toyotas reach truck as with most sit down reach trucks wont work in an aisle like this though.