Velocity is similar. If you were to run max in each you might see 100ish fps difference. The Norma is more efficient and case capacity is not consumed by the bullet. For all practical purposes, the cartridges are ballistic twins.
Regarding single vs repeater, I'd say it depends on your use of the rifle. For a dedicated long range rig there's no disadvantage to a single shot. Personally, I prefer my rifles maintain versatility and short range capability.
Consider a recent scenario. A hunting buddy runs single shots. He made a great shot on a muley at 1025. But, he hit a bit far back. When we got to the deer it jumped up and was disappearing over a cliff. He rushed his follow up shot and missed. While he fumbled to reload his single shot, I dropped the deer. If he had a magazine I wouldn't have had to.
In my opinion, there is no disadvantage to a magazine. So, why not? My partner claims his single shot is more rigid, more accurate. If it is, I don't see it in the field or at the range.