Well if I was at 23k miles with DL I would have minimal activity on the account once in a while to prevent miles from expiring (eg credit a short segment that does not matter too much for my FB account or move 1000 MR points...) and be patient. As soon as there is a fairly good oopportunity to redeem those miles (eg a domestic flight in the US or Europe or a DL upgrade, remembering that you can credit the earned miles to FB while using skymiles to upgrade), do it and forget about that account. Then only use that account as a one-off when it makes immediate sense (e.g. if you see a promo to transfer 75,000 MR, get 100,000 skypesos and know you can immediately book an award you want such as transatlantic business).