To be honest i used to run MH in veg then middle of veg flip to Hordilux HPS
and run it thru final veg and flowering stage , and also ran just HPS thru out all stages of veg and flower many will state that running hps in veg plants seem to stretch ?? tho i never had that issue my self PS: i thru away all my MH bulbs years ago
i can honestly say if asked what i would do it would be dual Arc bulb
since running the Hordilux Super blue dual arc bulb i have never looked back for veg and flowering stage i try to run 1 dual arc inbetween 2 HPS 1000 watts you should check out the Hordilux super blue dual arc only comes in 1000 watt and only can be run on magnetic ballests once you have done a grow with these bad boys you will through away all your MH bulbs the growth rates are ridiculous pricey bulb with one year guarantee but well worth the price
http://www.eyehortilux.com/products/hps/PerformanceSpecs/lu1000mhhtlen/62800