Old man, he's on an FE450 I think.
This is what I did to be able to swap sprockets without pulling the slider off.
I cut the slider, then glued the two pieces of it to to the swingarm with black rtv.
If you do this, make sure it's properly aligned and use tape to hold it fast until it dries.
Added benefit is that it stops the slider from slapping around.
I ran 17/47 on my 650 supermoto, had to file two teeth down a little bit to fit it.
I reckon 16/48 would be ok for dual sport use, but 15/48 would suit a FE450 better for all around riding.
Should be able to run 48 and a 14/15/16 with the same chain.
If you go too tall the gap between the gears especially 5th and 6th becomes annoying.