Unfortunately, for me there is no improvement after installing r251.
I experienced the biggest lags in the Sprite Editor (see this video). Nothing has changed with the update. It still takes about 4-6 seconds from the moment I double-click the sprite till the moment that little window with Image Points opens.
Toolbars are updating slowly. If there are many animations in the sprite, clicking between them is painfully slow....
Startup time ~30 seconds before and after the update.
The lag when opening events dialogs:
small projects: no lag
big project (1500 events, 15Mb size): 1-2 seconds lag
System: Windows 10, Version 10.0.16299 Build 16299
i5-7200U CPU 2.50GHz, 8Gb RAM, SSD
I did a clean install of r251, but I didn't restart Windows. Usually after the restart C2 works really well for a couple of days, and then things start slowing down..