I have a large IRA ($200k+) and my wife's is around $50k, both are a mix of vtsax and vtiax. Would it be advantageous for us to create new accounts with this contribution? I am buying the same investment whether it eventually converts to roth or stays in my IRA, so our overall net worth will be the same regardless, but it seems like if we have separate accounts and split between domestic and international (ie domestic in my new account, and international in the wife's new account) that we can shift a greater proportion into roth.
For example if we both open new tIRA and I put $5500 into VTSAX and my wife puts $5500 into VTIAX, and VTSAX does really well in 2018, then I can recharacterize my entire new tIRA into roth. The actual balance recharacterized to roth will be higher than if we had recharacterized the lower performing asset, and will also be higher than if I had to recharacterized a pro rated amount from my main tIRA.