The Sako 75 is very good shooter. I almost bought one myself (75 deluxe). I had the opportunity to test fire one and a Weatherby at the same time. I shot better groups with the Weatherby to my suprise. I also like the action on the weatherby slightly better. I got the Weatherby Mark V Deluxe in .300Wby mag.. I also have a Browning A-Bolt (.308 win.) and a Tikka Whitetail Hunter (.223 rem.). The Tikka and Sako do feel very similar. The Sako has a beefer and smoother action than the Tikka. With the long actions there was less binding with the Weatherby and Sako as compared to the Browning and Tikka.
As far as cartridge choice I can only recomend the .300 Wby mag.. They have about the same velocity. The .300 has about 500 ft/lbs of energy more than the 7mm. You'll be able to find ammo for the .300 Wby. more readily than the 7mm RUM. As well as a larger selection of bullets and weights (factory loads).