Help choosing double wing for BP/W

Hi,

I'm going to be taking a cavern course soon and plan on doing cave/full cave eventually (live in australia, takes a while to progress through the courses here). I'm not really sure how to estimate the wing size i'll need as i'll be diving a drysuit which i've never done so i don't have much of a reference point.

I am 6ft, ~165lbs, will be diving a dry bilaminate suit, with steel 12l tanks (~100s) each of which is about 9.5lbs negative when full (19 total) - even if i do 10.5s at some point those are still 9 lbs negative each.

Anybody have any views on either of these: Hollis C - Series 360 Doubles Wings [208.1250.045] - $200.00 : Cave Adventurers!, We will NOT be undersold!!! and Hollis X - Series Doubles Wing [208.1250.037] - $200.00 : Cave Adventurers!, We will NOT be undersold!!! (gives 37, 45, 55, or 60 as options).

Can anybody step me through how to calculate necessary lift with a drysuit? How positively buoyant are they when you have the minimum "i'm not getting squeezed" air in them? Obviously i am carrying a crapload of weight and presumably would need alot of lift to counteract that i'm just not sure how to factor the drysuit into it all. Thanks!

EDIT: The other question i had was (1) am i going to be so heavy that i should get an al backplate and (2) do most people use a separate backplate/harness for doubles or do you just switch wings (i'd prob switch around somewhat often). Doesn't cost much for a hog harness plus al backplate is all im thinking.

Wings [brands] are [like so many other pieces of gear] going to be a personal preference....I dive double 100's, 120's and 130's for caves and usually carry a small deco bottle also...I'm 6'4" and almost always wear wet suits.....I use a SS bp exclusively [DSS Long] and I use the following; 100's/Apex wtx4, 120's and 130's/DSS Torus 50 or 52 [can't remember what it's rated at]...I like the DSS wings better...For me they're lower profile, better made and trim me out easier....But you're going to get a lot of opinions about this so you'll have to try as many as possible to find what you like best.......