Following as I have 4 Vegas and am interested in others views, which will surely be varied. I love the Vegas by the way, which I realize doesn't answer your question - sorry, no experience with Hydra's to compare.
I have a 50 gallon tank, the first year I had a vega on it and had virtually no growth of my corals. I upgraded my vega to a hydra 52, and growth was noticed immediately! I would never recommend a vega to anyone, but I'd highly recommend the hydra. My $0.02..
+1
I had the exact same experience as di; little to no growth with Vegas for about 8 months. Upgraded them to Hydras and immediately started seeing results (within a couple of weeks). I wouldn't recommend Vegas to anyone with sps. Hydras are night and day better IMHO.
The 52s are technically better, but I only say that because it has more LEDs. I don't have any first hand experience with the regular hydras. Check the classifieds forum. People sell them all the time. Someone is trying to sell 3 right now. Perhaps he will entertain splitting the set up if you don't need 3.