A lot of things to consider. I think you will find some of the better 250w lamp products are nearly as bright as an older 575w lamp product. Just like a S4 575w can pretty much replace a 1000w older style
par can.
When I spec fixtures for an event, I make a list of priorities for the fixture and then find 2 - 3 best choices, then send those out for bid. I also include features that are "must have" so if the proposal comes back with something not on my list I can make sure it will have those features that are important to me.
For example, maybe I need a moving light with color mixing and framing shutters. I believe Vari and Clay Paky offer products with those features so I will include those features in the specifications. But if a vendor comes back with a Robe or Coemar product, I'll look at it to make sure it fills the bill.