Well theres no CMY mixing, which kinda sucks, but depending on your venue it may not matter. If you have the budget, I would go with the new Mac 700s. They have CMY color mixing and a 700w source. Both units do feature a butt load of optics and gobos, so it really depends on color and output.
I guess it depends upon your application and budget and how many channels on your desk you can sacrifice to movers.
From what I have seen in Australia, the 500’s are more common place than the 550’s and depending upon your application, the 500 might work for you.
Keep in mind that as a lot of the bigger production companies are buying the 700’s, many of them will be sell off their 500’ and 550’s. I would keep my eyes and ears open if I were you and also make some enquiries, so that when they come up for sale, you might be given the first opportunity.
There is also Pulse Enterprises in SA that do a range of movers that are based on current top line lights but are a cheaper alternative. I am not sure if they have a web site but if you wanted to PM or email me, I could pass it on to you. Their other details are:
Their 575W Show Spot lists a trade price of $5500 inclusive of GST
However, it is difficult to go past the Mac range, as it has become the benchmark here because of their price and features when compared to Clay Paky or Vari Lite. So whilst the Pulse Enterprise lights might be cheaper (although I do not know how they stack up in terms of feature or performance), you will probably not be able to compete with other companies that are quoting on shows and specifying Macs.
Robe might be another alternative but I really don’t know much about their range or cost.
Our church has some Mac 500s. Horrid fixtures I think. The Studio Spot CYM by High End is much better in my opinion. I haven't worked with a 550, I would assume it is better than the 500. I would also agree with everyone here, look into the 700 if it fits your budget. Also what is the intended use for the fixtures?
We had 12 and they spent more time on the repair bench than on the road. Glad we got rid of them. I hope the new 700 (due in soon) are better. If your need is definitely a 575 (no idea what lamp the 700 has) then I'd go with the Clay Paky (my preference) or the Robe, which is a really nice fixture but doesn't have as many features as the CP.