Going to upgrade to Metal Halide - what type?

I have a 75 gallon reef that is running 390W of Power Compact lights.
I'm going to upgrade to Metal Halide and have decided on 2 - 175W 10K
bulbs.

There seem to be various types of sockets for bulb out there (i.e.
mogul, dual socket, etc) What is best for reef and why?

I'm looking at a retro kit that has 2 mogul sockets, but am not sure
if these are the best.

Also, I've heard that halide bulbs need to be replaced every 6 months.
But I've seen some vendors claim their bulbs are good for 12 months.
Are their certain types of bulbs that last longer?


Thanks in advance for any advice,
Scott