One big note on moving from a current DL gold or plat Amex card to the Reserve card....if you upgrade that account to the Reserve card, rather than closing the old card account and opening a new reserve card account, your YTD spending on the gold/plat DL card will count toward the Reserve card's threshold.
I did this from a DL gold card to the Reserve card back in March; the DL gold card spending is still included in the YTD total for the miles boost (though I will only hit the 30k level this year, as I am not such as high spender, yet).