99 r1 oiln change time .. been using pro 4 but its been mentioned that semi synthetic might be better ...? opinions ?

Welcome to the forum.

Is the oil you were using fully sythntic then?

I would keep using it.

the semi - sythetic oil is for transfering engines from mineral oil to sythetic modern oils. or slightly older bikes.

AS long as its bike oil, car oil has additives that make it really slippery, and on a bike that can cause clutch slip.

Also with it being a new ish bike, it needs to be newer type of oil with an API rating of SG or later like SJ becasue of its additives will help modern bike engines.