theres a decent chance you can get the AMEX charge in the next few months. I know amex was sending me pre-approvals for green and gold @ 7 months history. I'd wait to see if they offer you something before apping though. Discover and FNBO also sent me pre-approvals around 6-7 months. so wait a month or so after you hit 6 months and see if anything comes up first.
EQ-736(08/14) TU-752(09/14) Newest to Oldest Barc Sallie Mae 6K | Citi TY Pref 4.5K | US Bank Cash+ 10K | Chase Freedom 11.7K | Disc It 10.5K | Amazon Store 2.5K | BOA Cash Rewards 10.5K | Closed Cards: 4 Oldest: 3yrs AAOA: 2yrs