How big of a t5? I have the 4' 8 bulb and love it! Can veg with MH. Would see things progress a bit faster, but can acquire bigger yields by vegging a little longer under the t5.
i found that in my 4ftx8ft veg tent i was happier with the results using 2 250w Metal halide lamps than the 2 4ft 8 bulb T5's I had first in there. The T5's worked and kept node growth short but i just feel the overall plant health and thickness of stems in veg I get from the Halides translate into sturdier plants that can support more bud in flower