BPT:
If there is anyway you can hold off and save until you have enough to get what you want--do it! You do not want any regrets that will just have you upgrading again if you feel you short-changed yourself.
Read all you can about the lenses, save your money, and buy the one you think is best for you. The LBA thing can be dealt with successfully, hang in there.
BTW, I selected the Tamron (and I'm delighted), after extensive research, but I never actually shot with the other lenses you are discussing here. Perhaps you can find a way to try the lens you want, first.