Another option is to learn to clone and put the clones into flower when they'll reach the maximum height you have. This opens your options to many traditional strains.
For example, germ a fem blueberry in a 16 oz cup of promix - this is your first mother - let it grow so you have a number of nodes to take clones from and top the plant to force branching, the top will be your first clone. Make a simple bubbler cloner, when they root transplant into 5 litre pots or into a hydro vegger if you want to grow hydro. After one grow you'll know the stretch for the strain you want to grow, let the clones veg to the height you need to max out your garden's height during flower - a stable blueberry might stretch from 8" to 12"-14" under a 3000K 600W MH, you'll figure it out for your set up.
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Another option is to do what Lostcoastlocal is suggesting - train the plants to grow horizontal instead of vertical. A few years back I bent 12 x 6'-8' sativas parralell to the floor then around their pots so just the buds stuck up vertically. It was like a marijuana Christmas wreath.
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42 w CFLs are going to rob you of yield, you may want to look at a low wattage HID or a T5 floro.
Have fun!