"ultimate" - I believe that changes with age and experience? I started out thinking 30-06 was end all and be all - because that is what my Dad used. Then to 308 Win. Then to 7x57. Latest one that I bought for myself to use is a Ruger Compact in 243 Win - I had bought two others previously in 243 Win, one for wife to use for her first deer and one for our grandson to use. My brother is two years younger than me - he has used a 300 Win Mag, for elk, moose, deer, wolf and sheep for 30 plus years - he got his rifle about the same time that I bought my 338 Win Mag. We have taken many dozen deer and elk in various parts of Saskatchewan with those cartridges - I am sure 15 feet to 300 yards, or so - at extremes. A lot is what you have used - I have never used 270 Win, 280 Rem, 25-06, etc. but know guys who will say those are "perfect" - often the only one they have ever used - and it works well. And we met an older dude in Northern Sask. who told us his 22 rimfire Magnum was the perfect deer cartridge / rifle for him - he was not terribly interested in regulations, licences, or seasons - just what worked best for him.