I went ahead and leveled my Dh's 5x for Shadowlands and rest of Bfa. In order to counter squish, I decided I'll put in more time to Bfa.

Given that the anniversary gives 15% xp and rep plus 10% more xp with bfa pots and heirlooms, I leveled from 98 to 120 just under 18 hours played (17 hours and 50 minutes or so). Usually, 45 mins per level. I do have flying and know the horde quests inside out so wasn't problem.

Overall, I'd definitely suggest leveling right now so you can take advantage of those anniversary buffs. Especially, if you have Darkmoon Faire on December 1st or so when it comes, you'll just steamroll thru levels regardless of what class. Don't forget, if you're leveling a brand new class from lv1 the Draenor part also has 20% added xp, so that's 200% xp almost. Just total domination

Just something to think about if you're planning to go retail/currently deciding to level up.