Four foot T5's generally put out something like 90+ lumens per watt, but most of the 4 ft tubes I have seen advertised are 54 watt while the 2 foot tubes are 24 watts. What is the square footage of the area you are growing in, if you plan to utilize all of that space? I am assuming 8' is the height of the room, in which case square footage would be 6 x 4 = 24 sq. feet. That is kind of a big grow room, so those tubes really are not going to cover such an area of flowering plants.
As I rule of thumb I have heard that 60 watts per square foot is more than sufficient. My plants are currently flowering in a room with roughly 50 watts per square foot, but it is just a small area(more like 3 x 3). If you went by that rule, those fluorescent lights might cover 8 sq. ft but in flowering I think even that would be pushing it. I would recommend you split the room into veg and bloom chambers, if possible, to take full advantage of that space and harvest continuously.
A roughly 2 x 4 (8 sq. ft) area flooded with fluorescent light for veg, and the remaining 16 square feet would be perfect space for a 1000 watt HID.
