Dogger,
Your Ruger in 7x57 is more than ideal for what you have in mind.
As other posters have said, the factory-supplied 140-grainer is marginal on paper, meaning that in an ideal world where only the best tool is used for the job you may want a bit more juice. Now, I have not had any experience with the Federal 175, but I would be optimistic based on their general reputation for quality.
And anyway, I am prepared to stake my reputation on the fact that even the 140-grain factory 7x57 would not give you any trouble in the actual field conditions you have described. Do not forget that the .275 Rigby, one of the most popular hunting rounds through the 1920's, was no other than a 7x57 with a 140-grain bullet.
But if you have access to reloads, you don't even have this problem. Top the case with a nice 160+grain spitzer (from Barnes, Nosler, Hornady or my personal favorite, Hawk) and do not lose any sleep over whether your quarry will perish promptly and humanely.
The late Bob Milek, in one of his last articles, argues passionately for the standard-velocity cartridges such as the 7x57 (one of his pet chamberings) as the ultimate for North America.
Sure, if you
want to have a reason to invest in another rifle of larger caliber (a .358, perhaps?), you have all my moral support! In the last 10 years or so, I have found about 40 reasons myself!
However, please don't feel undergunned with your 7x57, EVER. Provided that you don't ask it to do the impossible (stopping a pack of grizzlies in thick stuff or potting 'chucks ar 600 yards), you are in very good company with that caliber. In very good company indeed.