I have rarely run into anybody that swims 450 yards in just over 4 minutes, including college swim team members. IMHO, only the best college/Olympic 400 freestyle swimmers could swim 450 yards in 4:01-4:14, which is what I consider just over 4 minutes.
I was too slow to get a college scholarship in swimming. My best competitive stroke was breaststroke; I placed 9th or 10th in the 100 meter Breast at the Colorado State AAU Championships shortly after my 17th b-day (perhaps if I had done more than 2.5 months training per year). Shortly before my 18th b-day I "trained" a couple weeks and won the 50, 100 and 200 yard Free's in South Eastern Colorado's AAU Valley Championships; all of them qualify as flukes.
In the 100, I had a perfect start (read false start), three perfect flip turns (old school pike!) and won by two body lengths (probably 'cause the others all
knew I false started and hesitated on the blocks). My time was ~1:00. My 200 time was probably around 2:15 (the favorite with 8 second better time in prelims broke his foot on a flip turn - finished second, but got a scholarship). A 400 yard free in under 4 minutes as a serious training 17 year old
will result in a college scholarship. 450 yards in just over 4 minutes
is in the realm of the Olympic
Finals 400 swimmers.
In yards, the PADI requirement for 5 points is "less than 6 minutes." That is averaging just under 1:30 per 100 yards. This winter I "trained" for less than 10 days and managed ~5:55. That was my first swim training since that 2 week "wind sprint" training
over 32 years ago. I am
not trying to toot my own horn; I am trying to show how easy PADI is on DM's. I was not a good enough swimmer to get a college scholarship, have done no swim training for over 30 years and even on vacation at 7,200 feet above my residential elevation for the past 20 years (sea level - Los Alamos, NM) a 5 on the 400 only took 2 weeks of training.
450 yards in under 10 minutes sounds like a "reasonable bar" to me! Wish PADI would require similar, but that would seriously impact corporate and dive shop bottom lines.