Final gearing in 4th vs 5th will most likely be similar. The last gear doesn’t have the ability to pull. If they split up the ratio for the 5 speed then some final gearing changes could help the bike run in the 55 mph range but top speed won’t change. I can run 55 and pull to redline in 3rd on my monkey but I have to run 9K to hold 55 how long can you realistically do that for. FYI the rev limiter kicks in at 9.25k. Thats where the five speed may prove superior if it can be geared aftermarket to pull 55 say 8K in 4th the bike would be more useful in real life situation on the road. It’s too early to get real feedback from the Grom community, the 2022 Grom is five speed here in the USA. I’m thinking hard about the trail 70 when it finally gets released. Hope we see it in a 5 speed
My ideal setup would be to be able to pull top speed in the next to top gear and have top gear as an overdrive, for relaxed cruising. I can't quite do that on my 4 speed because the spacing is too far apart. 3rd gear is too short and 4th is too tall. My bike could do 65mph, but 60 is the best it'll do in 3rd, screaming it's head off, and 58 is the best it'll pull in 4th. However it cruises at 50 nicely and anything faster gets scary. The Monkey feels so much more solid at that speed, and would benefit with a close ratio 5 speed.