OK, having used BOTH the 30 and 45 now (the 30 is still in the rinse tank from this afternoons romp in the salt, and a buddy of mine dove the 45 this afternoon) here are my impressions.
1. There is NO - zip, zero, nada - difference in trim between the 30 and 45. This is simply amazing - Koplin has managed to do what Halcyon could not - design a wing that doesn't play the "butt game" when the lift goes up in size.
2. There is NO - zip, zero, nada - difference in EXTERIOR dimension (height x width) between the two wings.
3. The ENTIRE difference is in the inside bellows, which are completely protected by the TANK and thus virtually impossible to damage (e.g. think sides of wrecks, unruly speared fish, etc)
Both of these wings trim out and dive fabulously. Neither has any penalty (or benefit) over the other in terms of drag in the water that I can detect - both almost perfectly "disappear" when in use.
The only difference I can detect, having dove both - is the ultimate lift. You can literally ride the 45 like a RAFT on the surface. The 30 doesn't have enough lift for that, but it will happily float you mostly out of the water on your back.
My configuration for these dives is a single HP steel tank, 3 mil jumpsuit, 19cf pony, SS BP + STA (Halcyon BP and OMS STA), long hose with bungied backup. I need 2lbs of lead to sink me in this configuration.
For those who say the 45 is "too much", I say "bunk." That has, up to now, been predicated on the trade-offs you have had on
all the Halcyon products over 27lbs - both the 36 and 45s have had the expando-panels on the bottom outside of the wing.
This is not true for the Oxycheq, and does not apply to them. Both the 30 and 45 are perfectly fine, and there is no compelling reason to buy the lighter one on the basis of trim - at all.
I'm keeping both, but will probably dive the 45 most of the time, simply because I won't have to mess with anything as I change from wetsuit to dry. The 30 with AL plate is likely to end up being my g/f's BC of choice
The Halcyon Mousetrap has been trumped!