Ballistically-speaking, I remember seeing a report where about 18 to 18 1/2" of barrel will get all the velocity you can get out of a 22 LR round. After that, the bullet can actually start to slow a tad as it traverses more tube. But really, we're talking a .22 LR here. A few FPS here or there matters not for anything I intend to do with a .22. For a "keepsake" rifle, it has to feel good to you, and it has to make you smile every time you look at it! For me, that would probably mean a 20 or 21" barrel for the kind of rifle you're talking about.
