OP, Pretty much what 'burnthesheep' has pointed out.
The biggest gain you're gonna get is from your own position... and less so from the bike and parts. But, it's ok to get the marginal gains from the bike.
This was posted in another thread - emphasizes the importance of a position as wind resistance becomes more important - obviously from your post, a factor.
UCI Banned Road Bike Position Aerodynamics - it's really illustrative of the most common positions/postures, even outside of the 'banned' positions, on the aero of each... nice summary with numbers.
I haven't used deep cross-section aero wheelsets much (just for TT, which I don;t do much at all), but those whom I ride with say the most impacted they felt with crosswinds, were due to 50+mm deep wheels, hardly any comments on the 'frame'... So maybe some well designed 40 ish wheels might be a good compromise... which might impact on bike choice ?
Nice 'toroidal' design wheels would be a big complement..
Otherwise, I would consider your current Bike, the Roubaix, and think about what it is in that design which might make YOU more Aero, and still comfortable enough to do a whole ride in the best comfy/aero position you can achieve (or want to achieve). Then look at the bikes you have available to you, and see what matches best.
I like this site for comparing and considering bike/frame differences - very informative... especially using the 'Comparison engine'.
GeometryGeeks - pick your roubaix for comparisons with what you're considering.
another chance for 'analysis paralysis'.... LOL!
Ride On
Yuri