Another way of looking at the issue.
Assume $0 resale value after this period:
iPad 9.7
$279 / 2 years = $139.50/yr
$279 / 3 years = $93/yr
iPad Pro 10.5
$499 / 3 years = $166.33/yr
$499 / 4 years = $124.75/yr
$499 / 5 years = $99.80/yr
Assume $150 resale value for iPad 9.7 after 2-3 years and ~$200 resale value for iPad Pro 10.5 after 4-5 years or ~$300 after 3 years:
iPad 9.7
$129 / 2 years = $64.50/yr
$129 / 3 years = $43/yr
iPad Pro 10.5
$399 / 3 years = $133/yr
$299 / 4 years = $74.75/yr
$299 / 5 years = $59.80/yr
And what 2-5 years might mean in terms of iPad generations:
2017 - iPad Pro 10.5 A10X/4GB
2016 - iPad Pro 9.7 A9X/2GB
2015 - none (Pro 12.9 A9X/4GB, mini 4 A8/2GB)
2014 - iPad Air 2 A8X/2GB
2013 - iPad Air A7/1GB
late 2012 - iPad 4 A6X/1GB
early 2012 - iPad 3 A5X/1GB
2011 - iPad 2 A5/512MB
2010 - iPad A4/256MB
The iPad Air 2 is very well regarded in terms of longevity while maintaining performance but it should be noted that that model is only 3 years old.
Assume $0 resale value after this period:
iPad 9.7
$279 / 2 years = $139.50/yr
$279 / 3 years = $93/yr
iPad Pro 10.5
$499 / 3 years = $166.33/yr
$499 / 4 years = $124.75/yr
$499 / 5 years = $99.80/yr
Assume $150 resale value for iPad 9.7 after 2-3 years and ~$200 resale value for iPad Pro 10.5 after 4-5 years or ~$300 after 3 years:
iPad 9.7
$129 / 2 years = $64.50/yr
$129 / 3 years = $43/yr
iPad Pro 10.5
$399 / 3 years = $133/yr
$299 / 4 years = $74.75/yr
$299 / 5 years = $59.80/yr
And what 2-5 years might mean in terms of iPad generations:
2017 - iPad Pro 10.5 A10X/4GB
2016 - iPad Pro 9.7 A9X/2GB
2015 - none (Pro 12.9 A9X/4GB, mini 4 A8/2GB)
2014 - iPad Air 2 A8X/2GB
2013 - iPad Air A7/1GB
late 2012 - iPad 4 A6X/1GB
early 2012 - iPad 3 A5X/1GB
2011 - iPad 2 A5/512MB
2010 - iPad A4/256MB
The iPad Air 2 is very well regarded in terms of longevity while maintaining performance but it should be noted that that model is only 3 years old.