I would get the 22" , instead of the 34" , a 34" t5 in a 40 gal will make it near impossible to create a UVB gradient with a 34" bulb in an enclosure thats 36" in length. The idea is to recreate a gradient , so that when your dragon wants high levels of UV it has that option , as well as the option to escape the UV, just like we do with the heat. The only difference is the tool that it takes to measure UV levels is much more expensive, and not as readily available as a thermometer or temp guns , so we have to rely on the testing results of those who do have solarmeters to double check their work. It is ideal for your heat gradient to overlap with your UV gradient as well , as to mimic the sun as much as possible. A 34" fixture will also greatly limit your ability to expand vertically without getting too close to the UV bulb. You don't want your dragon to get much closer to the UV source then 12"
As to the two lower watt basking bulbs , i dont see any issue with that as long as your temps are in line. Basking bulbs are much simpler to mess with.