So I created a new paragon calculator showing you your new XP at the end of season and how much XP or paragons you earn when you complete a Greater Rift.
Paragon Season Converter: https://clanaf.info/tools/index.php
Paragon XP Table (up to P3000): https://clanaf.info/tools/paragon.php
Paragon & XP Tool for GRifts: https://clanaf.info/tools/griftxp.php
XP calculator: https://clanaf.info/tools/xpcalc.php
The GRifts XP tool is very cool cause it will display what your new Paragon and XP when you turn in a GR.
For example, if you were a fresh new 70 @ 0 paragon and lets say you got carried into a Tier 70 GR.
Besides the GR mob XP, the turn in will earn you a new paragon of 103, GR80 would make you P157, GR90 = P231 and GR100 = 323
Let me know if you feel the math is wrong, but im am 99.99% sure it is right.
Some credit goes to this post http://www.diablofans.com/forums/diablo-iii-general-forums/diablo-iii-general-discussion/130338-paragon-10000 by Bagstone, I used his data for the calculations
I've created an excel file calculator for best GR level to chose in order to get most XP/hour ratio. Check it out and let me know what do you think
(description to excel in youtube video - link to download in youtube video description)
Hope it helps!