I've had an old model (tang safety) Ruger M77R Ultra Light with 20" barrel for over ten years and absolutely love it. With a Leupold Vari-X III 2.5-8 scope on it, it feels like totin' a .22 rimfire. SOOOO light and handy!!! What Lone Star said about the load pressures is correct. Factory loads and most all published load data is lower pressure to be safe in the Sav 99's. In my Ruger, I've found that if you work up carefully in 1/2 grain increments and watch for pressure signs, you can usually up the loads somewhat.
I've used as my guide the published charge differences between standard and +P .257 Roberts loads for given powders or closely related powders. BUT, you can't just jump ahead and go right to your desired +P load!! You've GOT to work up to it slowly and carefully!!
As far as killing power goes, I've been amazed at how much better the .250 Sav kills compared to the .243 on deer, when the shot is at some angle other than pure broadside, IF you are using bullets of at least 100gr. The bullets seem to hold together and penetrate deeper and truer, while still creating a very effective wound channel, but without ruining a bunch of meat. And you can get excellent performance out of standard grade bullets. That said, a 120gr Speer Grand Slam out of my little .250 will take deer from any angle that anything else .30 cal and smaller will.
Right now, I'm working up a flat-shooting 100gr load to take to Wyoming speed-goat hunting. This particular rifle is a little finicky about the loads it likes, and it has quite a bit of upwards pressure against the barrel from the fore-end, so I'm gonna experiment with the bedding to see if that calms it down some.