...I know my lift requirements will be different in warm vs. cold based on the weight equations, but diving warm in a 30 pound wing shouldn’t be overkill right?
A 25 - 30 lb wing is quite standard, so it's not overkill at all for single tank diving with less or more weighting requirements (ex warm/cold water exposure protection).
You have weighting distribution options with any composition bp, so which you choose is really just personal preference.
Personally, I'm happy with my Halcyon AL bp with the Eclipse wing with 30 lbs lift for both traveling and local cold water diving. My small bp weighs 1.8 lbs as opposed to 5 lbs for the small ss, so it's a little lighter for traveling. The standard ss bp is 6 lbs.
For local cold water, you can insert a 6 lb STA (Single Tank Adapter) weight into a Halcyon STA (and maybe others). With an AL bp, that would be 8 lbs right there in your bp. You can remove the weight for traveling.
For local cold water, I use steel 80's, so I use very little weight. When traveling to warm water, I can use AL or steel tanks and not be overweighted.
You can also place weight pockets onto your upper and lower tank cambands for more weight or for distribution.
We're talking about 4 lbs difference between the AL and SS bp (all of your other likely ss hardware on it being the same), so it's not a lot of a difference.
For slinging a bottle, you want to make sure you have ss d-rings, which many of them do.