The 2mm you cite isn't the thickest part. Other than low end wetsuits the manufacturers are mixing thickneses in different areas - thicker in the front torso (for more buoyancy) thinner over shoulders for flexibility, etc.
The 2mm is most probably over the shoulders / outer side of the arm.

Something to note is what the leg construction is - a number of makers use 5mm on the thighs to lift the legs of typical triathletes (not swimmers by background - 85% have run/ bike backgrounds is a figure I've seen - from Huub - when they 1st set up).

What I've seen with few 'proper swimers' is the suits with higher leg buoyancy, esp. In the legs, don't suit them - they bend them backwards like a banana.
(I recall guy who's raced with our tri club - ex Olympic swimmer - taking a wetsuit off after a relay race and saying how wetsuits messed up his position and hurt their back etc for that exact reason. (Try swimming with one of those massive pull bouys as a comparison- if I try one I get pains in my back after about 2 lengths)

For Orca they push 3 'series' of suits dependjng on how you naturally lay in the water. Think the Alpha is for 'proper' swimmers.

Huub as an example have their 5:3 series for sinking legs people and their 4:4 for natural swimmers.
And 3:3 for some of their women's suits as higher bouyancy didnt help they claim.

There was a good article on the main site about one year ago on wetsuits. I swam through college and the info in the article informed my decision. That being said, I bought an orca equip (against the advice of the article). After reading the article, I was able to make an informed decision on what type of wetsuit I would like. I’m happy with the wetsuit,

You should be fine temperature wise.

Thanks for the advice! I'll take a look at the Huub 4:4 wetsuits and a further look at the Orca Alpha.

I also found this thread where they talk about testing swim efficiency of wetsuits through lactic and breath analysis. It seems that the Huub suits did very well, however most of their test subjects were triathletes with various swimming issues.

All of the swimmers I know use the same wetsuits as the rest of us. There's nothing special about a wetsuit for a better swimmer.

Pick the suit that fits the best.

Sleeved suits can be faster than non sleeved but not because of buoyancy, you'll almost always have one arm out of the water and the 2mm of neoprene on the arms isn't much. They'll be faster due to less drag from the armholes. How significant that is, is up to you but I wouldn't be looking at any more than 5 seconds per hundred. That is significant to a lot of people though.

+ 1 on Fit. With that in mind, the quality of the rubber grade makes a HUGE difference in fit, as the best grades have significantly more stretch. The liner material and how the seams are constructed, and pattern cut also effect this.
Personally, I think ROKA, which is a company founded by a couple of top D1 swimmers, have done the best job of making suits that fit a large range of swimmers really well. They also have fantastic customer service and a super easy return policy, making it hassle free to test out suits and return anything that does not work. Their “Pro” level and up have the most stretch of any suits I have dried, making it possible to have a tight fit without feeling constricted.