1. Parts 2 and 4 are a ton of xp and make those levels fly by.
2. The end reward voice of the master +5% xp = 213,000 xp (4,378,500 xp needed to hit 20 on a legend TR)
is something I believe should be factored in as it effectively makes all your other packs worth more XP, forever.
Reign of Madness is good XP and I rather like the chain, story and all, it's fun. So I would definately put it on the things to buy at some point list. But I would think Deleras would still be my first choice if I had to do it over again.