I would not feel undergunned anywhere in N America with a mosin and S&B 180 grain SP's. If I felt I needed more I would use some of the 200 grain stuff. They both kill deer most rikky tik. Yep, I like my mosins, of course I like my Marlin 30-30's alot as well
The oldest service cartridge still in common usage is the 7.62x54R. Must be a reason for it. Mosin nagants (1891) are still in use and are found on today's battle field. Must be a reason for it.
Sportrizing? I gotta agree that its cheaper to buy something already in that configuration. Want something unique and all yours? Do it, but remember not everybody will be willing to pay the price if resale is the motive. Just saying. Some reworks are pretty nice though. Have fun!