FWIW (in V2.0) I currently have 1692806 messages in my d-i-y group?
Opening FA is still (on this ancient clutter filled box with no free disk space) pretty quick, as it is moving between groups or messages etc.
It's even slightly longer delays that can impact the most (you feel like you are going backwards, even if there may be *extra* features you may or may not enjoy).
Cheers, T i m