Is this trip just for you, or more than one pax? With this number of Avios you could book a straight redemption in CW both ways. If two people, then an
Amex 241 redemption would do that, too.
Miami can be difficult for CW Avios seats (almost impossible in First without other instruments), and the upgrades from WTP come out of the same buckets. However, you could have some creative routing to get your long haul into Club if there's availability from say NYC, ATL, DFW etc. Additionally, WT-WTP is probably not a great use of Avios. It can still be quite a lot, so if you could book WTP both ways, then I think you'd be better off. Incidentally, there are sometimes some great WTP deals if you can start in Europe.
Also, always check that there's availability on the exact flights you want to upgrade before booking. You can do this but searching for straight redemptions on ba.com.
People here are quick to respond and have wealth of information (much more than me!) so just ask if you have any questions.