I finished the quest at lvl 41. I died once in the feerott from being abit cocky and not respecting the mobs basicly....it happens.
Far as the stackability of the boots its not that great. My paladin freebie horse gives a 10% run speed boost. When I equiped quested jboots I got 10% to my speed. Then I casted my horse it stayed 10%, so basically it does not stack with the paladin freebie lvl 20 horse spell. I can't say for sure, but I imagine it does not stack with purchased horses either. I heard at one point in time it all stacked, but that it was nerfed a long time ago (back around the era when heroics was ^^ not ^^^ and you had to do quests to access new tier zones.
Also when I kick in run it always goes to 40%. Even with jboots it does not go past 40%, so jboots don't help in that situation either.
I don't know if it stacks with speed buffs like sow, bard songs, etc etc. I have yet to buy a horse, I am too close to the carpet now to spend half my status and half my life savings for a 25%ish horse.
The obvious advantage over heritage jboots and /claimed jboots is the stats. Claimed jboots to my understanding have no stats? Also we obviously all don't have the jboots to claim either.
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Hi