My take on this question comes down to the real question, is the group size that the gun and ammunition together can do a large percentage of the actual group size that you are shooting. If that group size is 50% or more of the group size that you are currently shooting then the gun/ammo is likely to be playing a significant part in you overall result, that is the time to be looking for a better combination. Of course you will get to the point where there is not a better gun/ammo combination avilable to you, either through cost or the fact that you have the best pistol avilable with the best ammo, and any more improvement is going to be down to you. Hopefully by then you are the World and Olympic champion.
Alan