First off, let me say this...I own rifles chambered from .17 HMR up to .45-70...So this is just me going off of statistics, vs bias opinion as to which caliber I would prefer. I'll save my biased opinion for the very end of the post.
I feel there would be very little difference in wind deflection. The slightly heavier weight of the .30 is contradicted by it's larger diameter which is not as slippery in the wind, thanks to a greater surface area. The smaller diameter 7mm that is a little lighter, will be a little more slippery but is also a lighter weight bullet.
I would be willing to bet they would be so close in performance at 1000 yards, that the only way you could tell the difference would be to shoot them mechanically in a fixed rest, without human error. And even then I doubt you would see any sort of significant difference in wind deflection.
But that is my opinion, i'm not a human ballistics computer.
I also don't own either caliber, just going off of basic statistics and common equation properties such as diameter, weight, length, velocity, etc...
Now for the bias...
Since there would be no real difference, I would go with the 7mm WSM, but I'm also a bigger fan of the 7mm calibers than I am the .30's. Althought I do own a number of different .30 caliber rifles in several differnt chamberings. I like them both, and you wouldn't go wrong with either caliber, but my bias pushes me towards 7mm calibers.