If you going to buy a 300win mag or something similar in a Tikka or Sako 85 (especially fin lite), be aware that the kick will be pretty severe on it.
It really depends on that you are having problems with.
If your having trouble hitting game at long range from wind, either better wind reading or a better flying bullet will help.
It your having trouble seeing the game through your scope then a higher magnification scope will be the one.
If you are hitting deer but they running off still and not dead nearly instantly then a bigger round would be the ticket.
If your having trouble just hitting them more practice in windy conditions might be enough to solve all your problems without having to buy a new rifle.
Any idea on what sort of wind conditions you have to contend with in Scotland? (as is wind speed as I know it gets mighty windy there).