If cost isn't a factor then a dedicates .22 LR upper would be great. I like practicing with my same optics, so I would think an dedicated upper would be best for practice with the same optics as your .223. Maybe you use iron sights on both.
I Don't use iron sights, I am a bit concerned with shooting .22lr down my match barrel and compensator. I don't know if that is very good for it. I think I would put the same optics on both setups though.