You would see a big increase if you used a SSD as a boot drive, no mechanical drive can match them for 4k read/writes, and this is where OS stuff is done mainly.
And go for the size u deem fit enough, i personally use a 40gb one as i never go over 30gb on a OS/App partition, so i did'nt need a bigger drive, some like to add games to the SSD, this is where bigger ones help.
But the raptors would be good for game drives.