You're within the limitations of SharePoint (http://technet.microsoft.com/en-us/library/cc262787.aspx) in either scenario, which is good. Some of my thoughts
As far as performance, I don't think you'll see much in way of improvement going from one DB to multiple DBs, unless you can move the DB files to different disk arrays.
100GB is a reasonable size for one DB. MS recommends 200GB max, but the recommendation is for management of the dbs (harder to backup/restore, times get longer)
Using unique site collections also bring along some features or headaches, depending on what you require
- Unique permissions
- Unique quotas
- Roll up data is tougher (especially on SP2010)
- Unique DBs
- No central navigation (unless you use managed metadata)
And there's more in a post I wrote a while back: http://sp365.co.uk/2012/01/initial-topology-planning-site-collections-vs-subsites/
HTH, let me know if you have further questions