To understand the actions and career of Sulla, one must also
consider political events that took place during his youth, i.e. the initiatives
and fate of the Gracchi -- especially of Gaius Gracchus, when Sulla would have been
about 17 years old.
While historians differ on when the "Roman Revolution" began, it might be useful for the upcoming book chat on Sulla, the Fortunate by G.P. Baker -- especially as Baker presents us with a highly individualistic rambling through history -- to familiarize oneself again with the Gracchi, or even going back a further, as Baker indeed does. A convenient place would be From the Gracchi to Nero by H.H. Scullard which we recently read, and, if you have easy access to the earlier volume: A History of the Roman World 753 to 146 BC.
I happen to own a small German biography, Sulla, Eine Politische Karriere by Karl Christ, München: Beck 2002, ISBN 3406492851. Christ is firmly grounded in the Mommsen "Revolution" camp. Bryn Mawr Classical Review 2003.03.08.
The only other biography which I could find on Sulla, Sulla; The last Republican by A. Keaveney (Bryn Mawr Classical Review 2006.01.13), is still in the mail.