Zoom out at the end of each turn so that the galaxy is shown in tactical mode (all objects are displayed as icons) - easier when you can use a mouse wheel to do it (the zoom level for tactical map mode can be adjusted in the settings). Ships move faster and 1-to-1 ship battles are over more quickly. I play zoomed out nearly all the time with games which have many ships - it slows down ridiculously over some areas of ships [EDIT - and much more for some races' ships than others].
I have returned to playing GalCivII with megaevents on, and my game doesn't freeze so often when I exit (don't use the escape button to open the menus). The only problem is zooming while moving the cursor; this causes a scroll to the corner of the galaxy map which can last for several minutes.
Also, you can spot resources more easily. Zooming with the cursor over the mini-map will zoom the mini-map.
Zooming with a mouse wheel can also be done on the tech tree in the research screen, and on message boxes (such as starbase upgrades) without having to aim the cursor on a side scroll-bar.
