Ok, here's what I just tried.

I did Act 1 (I didn't time this) - but I did this fast, skipped as much trash as possible, didn't open any normal chests. This probably took me at least 20-30 mins
Festering Woods (3 - 5 elites)
Leorics (1-3 elites)
Cemetery of the forsaken (3 - 5 elites)
Northern Highlands (1 elite), then (Go to watchtower [if it's up] - top west 1-4 elites)
Highlands crossing (North to Cave of Moon Clan 1- 3 elites)


Then after I was done farming Act I - which was about 2/3rd of a bag full of rares (no bosses).

I went to Whimsyshire - with 5 stacks.

I cleared it, it took me exactly 40 minutes. There were 6 packs, and 1 purple. Which filled up the last 1/3rd of my bag.

In Whyimsyshire, I got 4 level 63's and 1 legendary.

In Act 1, I got 3 level 63's.

The nice thing about farming Act 1, is that you get 5 stacks to go to Whimsyshire.