Any recommendations for what manufactured ammo works best for a) target shooting and b) hunting deer?

I had a 6.5 in Swedish Mauser in the early 80s. Only 6.5 ammo available then was Norma. I bought several boxes of what was available probably 140 grain. I reloaded with 120 grain spitzers if I remember correctly. !40 grain could potentially give the best target accuracy. 120 grain is entirely adequate for our small white tails. Other parts of the country where they grow big white tails you might want something in the middle.

Software changes spitzers to spritzers unless you force it back!

Looked at your location and see you are in Canada, you may have much larger deer up there. You should be good with 130 to 140 grains. I heard it said the white tail deer here is genetically the same as the larger midwestern deer. Our summers are brutal and limit their appetite, I know my cat does not eat as much in the summer. :-)

In my 6.5 x 55 Swedish Mauser, 140 grain bullets are the most accurate. 120 grain bullets are very accurate at 100 yards, but less so at 300. PPU makes some very accurate ammo, in both hunting and match bullets.