6.5mm bullets have the highest bc and the short magnums supposedly burn powder more efficiently then the longer cases. I wanted a 6.5 saum but have heard issues with the brass prep so wanted to do a project 6.5 wsm. You can keep your scar last time I had orders to Cali I called ca doj and they allowed me to bring my ar in just had to take my orders to the local pd or sheriff and pay the registration if your not a ca resident.

Beekeeper,

What are the parameters you're setting for yourself with this rifle?  It seems from your posts that cost may be an issue correct me if i'm wrong.  If your wife was upset at the cost of the SCAR then it may benefit you to sell it and put that money towards a dedicated long range rig.  Some questions did pop up after reading your post.  Do you reload? Is this strictly a target rifle or combo rifle i.e. target/hunt/comp etc? Is it weight sensitive etc?  If cost is an issue with your wife then the 338 lapua wouldn't be a front runner also the ultra mags and their wildcats I.e. Edge unless you have a stash of brass available. I have or had all of them and some other hotrod wildcats including also the 6.5 saum which was mentioned by kong and its an awesome round.  If you're worried about barrel life then maybe checkout either a 300 or 338 Norma Mag which I have as well, supremely accurate and great barrel life. As well as great high BC bullets available for those calibers.

There's many great long range calibers out there but you need to determine what are your operating parameter's so you can research what will fit your use best.  Another issue is recoil? how do you deal with it? Its a big difference between a 6mm and a 338 per se.  Also, if you want a custom built rifle or just a factory one?  I know lots a questions but trust me it helps to ensure you end up with what you really want.

Wish you the best in your move to Cali...Aloha

If you are just going to target shoot or plink long range, I'd go with a smaller round.  .308 will go 1K, but it'll take skill.  6mm, 6.5, 7mm....  Higher BCs, less recoil, and less expense to shoot more.  You are going to want to get into reloading to get the most out an expensive or custom long range rig.  Get the best optic you can afford. 

accurateshooter.com has tons of information and knowledge, check out f-class.