Help Selecting a Head: M20/BH-55/AS Z1?

After much assistance from this forum I am leaning toward a Gitzo Systematic tripod GT3531S.

My next decision is which full size ball head to get. I don't have any experience with these so I wanted to get everyones pros and cons (I also realize that to a certain extent this becomes a personal choice).

I have read good things about the: Markins M20, Really Right Stuff BH-55, and the Arca Swiss Z1. Are there others that I should consider? Anyone have any info on the Gitzo Systematic head?

The heads are somewhat similar but do have some differences:

Model__$__Weight_Heigh​t_Base Dia._Ball Size
M20___360_1.25#___3.98​"__2.68"______48mm
BH-55_355_1.6#____3.65"__​2.86"______55mm
AS Z1_365_1.2#____4"_____​2.7"_____Eliptical

I am planning on using this with a 5Dii and the longest lens would be a 70-200 f2.8 + 2x extender (at least for now). I will also probably get RRS QR plates (which everyone seems to rave about) including an L bracket for the camera.
Thanks.

If the longest lens you're going to use is a 70-200 are you sure you need the M20 or equivalent? I have an M-10 and it does quite nicely with a 300mm f/4 lens mounted. I'm sure overkill wouldn't hurt, mind, you'd never wonder if you would have benefited from going one up... at any rate, I can highly recommend Markins for quality of construction and ease of use/performance - have used the M-10 for >12 months now and can't recommend it highly enough. I haven't used any other ball heads other than a Manfrotto 488RC2, mind you - not the most experienced judgement.

Oh but the M20 just looks sooo good on a 3 series gitzo!