Also, it shouldnt be a problem if I use, for example, an 8 speed bar end shifter with my 6 speed cassette right?
Nobody seems to have mentioned that an 8-speed indexed bar end shifter won't work with a 6-speed cassette because the sprocket spacing is different. If you switch to friction mode, you won't have a bunch of slack cable because the total cable pull for 8-speed is about the same as the total for 6-speed. The excess should be at the low gear end of the lever travel, so that the cable doesn't go completely slack in top gear.
Nobody seems to have mentioned that an 8-speed indexed bar end shifter won't work with a 6-speed cassette because the sprocket spacing is different. If you switch to friction mode, you won't have a bunch of slack cable because the total cable pull for 8-speed is about the same as the total for 6-speed. The excess should be at the low gear end of the lever travel, so that the cable doesn't go completely slack in top gear.