Hey, I am not very familiar with SMLE's, but if it is accurate, dependable, and has decent magazine capacity you wouldn't go wrong either way. It's tough to decide whether to buy new firearms or just stock up on ammo. I know it's tough but i'm in favor of both LOL.
I just got rid of a Kimber 8400 in .300 WSM because I never saw ammo for it anywhere but gun shops.
I feel best about sticking with more common ammo. I personally like 30-06, .308, and 270. I want a rifle for each of those calibers. So I have a 30-06 M77. I sold the Kimber and picked up a .308 Ruger Gunsite Scout last week (10 round magazine, flash hider, picatinny rail, mauser style action). Now I want a good 270 semi-auto like an AR, AK, or Mini. That's my plan FWIW. Just food for thought