I've noticed that when the history gets large, speedcrunch is slow to open and slow to produce results of calculations.
My history file is 1Mb in size, and this causes speedcrunch to freeze for 3-4 seconds for each calculation.
You can of course clear the history periodically, and this does restore full speed, but my suggestion would be an option to limit history to the last x number of entries. This would ensure you always have recent history and good performance.
For reference: Version 0.12 running on an SSD on Windows 10.