Sweet! Very nice group. I do indeed like the 6.5x55.
Now on to your question.
A big thing to consider is availability of ammo for your type of shooting. If you will be handloading, and care nothing of factory ammo, then I might suggest the 7mm, as sierra has some new bullets that are amazing in that caliber (of course, still not as amazing as the 6.5's). But if you need factory loads, then I think you will be better off with the .300 Win Mag. Federal (which you might have a hard time finding over there) makes a great match load for .300 Win Mag (190gr Matchking at 2900 fps) that is fantastic for long range shooting. There are other .300 WM factory loads that work very well for long range also.
Personally, I like .300 Win Mag better, but thats a personal opinion.
MEL
Now on to your question.
A big thing to consider is availability of ammo for your type of shooting. If you will be handloading, and care nothing of factory ammo, then I might suggest the 7mm, as sierra has some new bullets that are amazing in that caliber (of course, still not as amazing as the 6.5's). But if you need factory loads, then I think you will be better off with the .300 Win Mag. Federal (which you might have a hard time finding over there) makes a great match load for .300 Win Mag (190gr Matchking at 2900 fps) that is fantastic for long range shooting. There are other .300 WM factory loads that work very well for long range also.
Personally, I like .300 Win Mag better, but thats a personal opinion.
MEL