Lithium 2018 (vs 2017?)

[PusherII]

I'm pretty sure i will buy a 10 and 14 lithium and here a question for you guys.
As you may know, in 2018 airush released 3 different models of the same lithium kite. Difference is basically in quality build

lithium progresion is let's say for beginner (less quality)
lithium progresion sps (intermediate quality)
lithium core (better quality over previous two)

My doubt is if i would go better with a progressione sps that is way cheaper (and lot used offers), or 2017 brand new model where i still can find some very good deal. 2017 lithium is unique model, so i could expect is the equivalent of 2018 lithium core....or not?? in that case, would be a no brainer 2017 choice...but maybe here there is somebody has a better knowledge about that