In my 24" .338 Norma, using 88 grains of H1000 I got HBN coated 300 Bergers to 2675, with this load according to quickload I was just under the 63,000 PSI limit that CIP established for the cartridge, if using a naked bullet, with the HBN coating I can usually go another 1-1.5 grains in a case this size to achieve the same pressure as a naked bullet, so I was likely well under that. Using Retumbo, velocity may go up a little, and according to quick load N570 would get around 2730 fps with a naked bullet at CIP max. With the 285 Hammer Hunter, I got up to 2800 fps using H1000, and with the 270 Badland Bulldozer my load is 2820 fps with Retumbo, and 2850 fps with VV N570. Also tried the 265 ABLR, got them up to 2900 or just shy with H1000, RL26, Retumbo, and IMR7828SSC, and all still had a little room to go. I think max CIP would be around 2900-2950, depending on which powder.
In a 28" barreled 338 Norma I put together for my buddy, with a light load of 86.5 grains, the 300 Berger is going 2730 fps. With the same 88 grain load, velocity is 2775, and 89 grains is 2810. Retumbo got the 300 Berger up to 2825 with a well established load.
For a hunting/repeater rifle, the .338 Norma is a better fit. My OAL with a 300 Berger seated with the bearing surface/boat tail junction at the neck/shoulder junction of the case (which happens to also be .020 off) is 2.680, and fits jn a standard non modified long action, as it was designed. A .338 lapua with the same bullet and the same seating limitations will be significantly hindered due to the bullet being way down in the powder column, and will have no significant advantage over the Norma. If the Lapua is set up as a long range target rig, single loaded and throated properly, an increase of 50-100 fps over the Norma is likely with equal length barrels.
From what I have personally seen and read, it seems that the Norma handles shorter barrels better than the Lapua. There is limited factual data for this, just the fact that most people have the Norma's with a 22-26" tubes, and the Lapua's tend to have 26-32" tubes, hence why the Lapua is generally labeled as a much more powerful round. It is a little bit more when seated properly, but 4" of barrel make a bigger difference.
As far as brass if you reload, Lapua and Peterson both make high quality, tough brass.
As far as factory ammo availability, you will have to answer that. Start shopping around and see what you find more of on the shelves, and if the quantity of ammo you can find is satisfactory. I personally reload exclusively, so I honestly never even look at the ammo shelves.
Bottom line, the Norma is a better hunting gun round. The Lapua is a better long range gun round. Just my opinion, backed by a few factual points, mostly linked to seating and cartridge OAL. Hope this novel helped some.