Depending on how mechanically-inclined you are, it would be more beneficial to just get higher tyres instead of swapping the transmission. Anyway, you could maybe keep the 4-speed and do some gear swaps when it needs some sort of refurbishment.
I'm still favorable to 4-speed transmissions, if we consider that the current 5-speed and 6-speed are getting more focused on meeting the EPA test method than on an overall efficiency in real-world conditions.
workaround ideas to discuss among friends: Is a 4-speed manual transmission really that bad?