Its been some time since I shot or bought any factory loads. BUT, some time back I chronod some 158 Federal Hydra shok in a Marlin lever. IIRC I was getting 1600+- fps. Generally all factory magnum pistol loads are rated from a short, vented barrel, so the vel increase from a rifle/carbine barrel really jumps. Personally, I don't think you will get anywhere near 2000 from a 158 factory load, maybe a 125gr.
CW