First of all, I'm new here so I'd like to say hello to everyone

Secondly, I'd like to get some advice on upgrading my front brake in my bike. Right now I have Avid BB5 160mm both front and rear and I'm looking for some more power and modulation, so I came up with an idea of buying hydraulic brakes.
I'm seriously thinking about XT for the front (for the back I'll buy later) together with a 180/160mm XT rotor ...or Avid Elixir CR which is a bit more expensive.
I'm not cycling in winter time, so the disadvantage of mineral oil isn't important. What I like in XT is Servo Wave and I guess it's a major advantage because I've read that the pads in Elixir CR are pretty close to the rotor (closer than in XT) and can make noise sometimes.
I know that there was a million or more threads similar to this, but I just can't decide which one to choose, so any help or advice would be really great.

Finally, I'd like to know whether I need a bigger (180mm) rotor or is 160mm enough? (I weigh 75kg, my fork Marzocchi MX Bomber so rather no worries)