it might be possible for the strawhats to fight Buggy&Saint Shanks crew at the same time.
like:
Luffy vs Saint Shanks & Buggy , well Luffy can knock down Buggy before he get to clash with Saint Shanks.
Zoro vs Mihawk
Sanji vs Beckman
Yamato vs Lucky Roo
Jinbe vs Crocodile
Usopp vs Yasopp
don't care about the rest too much.
it will be like just friendly duels after all with some comical scenes thanks to Buggy and his crew