Version 6 is currently reported to be four times faster than version 4, along with the process for finding files has been streamlined.
Community Manager Mikeal Rogers says:
Imports [of code modules] and startup time [are] dramatically faster than it used to be.
Version 6 is now the current release line, turning it into the LTS (Long Term Support) release this fall. Version 5 will be maintained for a few more months, and version 4, the current LTS release, goes to maintenance mode in a year, with only critical bugs, security fixes, and documentation updates permitted.