Caltex 98 Fuel vs BP Ultimate 98 Cold Start Issues

Hey guys,
 
Recently I was having some cold start issues with my MR2 (Japanese 1990 MR2 Turbo) The car is also stock apart from a 3" exhaust. On start up the car would either really struggle to turn over, it would sit at the point of just before stalling - stuttering for like 5 seconds before either finally turning over or stalling altogether. The other option was it would not turn over on the first try, but one the second attempt, it was fine.
 
I read somewhere about someone having an issue similar and someone suggested changing different fuels. I usually (95% of the time) fill up with Caltex 98, as the servo around the corner from my house is a Caltex. So recently I switched to BP Ultimate and it is safe to say that the problem has happened since, even with the weather getting colder.
 
So I guess this is kind of a heads up? As well as a question if anyone else has had similar issues? Maybe something worth looking at if you're having similar problems. :)