In BigBox....>Options >Image Cache. If you run the image cache for all your images and let it finish generating the full cache this helps speed things up. It is not the end all to issues users may have, but it helps BB run smoother once the cache is built.
Our two devs do constantly develop for performance, in fact the latest beta has more improvements. LB/BB are WPF programs and therefore put a lot of data into memory, so the more RAM you have the better. 4GB is not recommended, so 8GB should be enough to run smoothly. With 8GB though I would say use less transition heavy themes. If you use the Default theme I would recommend reducing some of the theme transitions if you are having issues. These are located in the >Options >Transitions setting in BB.
You can read some information on performance from one of our devs here.