I've tryed doing this multitabling. I ran 1.4BB/100 over 30K hands at 2/4$ my winrate 3-4 tabling was around 2.5bb/100 over 10K hands so none of these samples are very big but they still show how your hourly BB/100 is indeed bigger when multitabling.

@Jeff. I think theres a calc fault in your post as you think the hourly winrate go from 57$ to 114$

4 tabling:
doing 240 hands an hour is 2,4BB * 3BB/100 = 6,8BB/hour = 39$

8 tabling:
Doing 480 hands an hour is 4,8BB * 2BB/100 = 9,6BB/hour =57$

Say you keepup the 4BB/100 while 4 tabling then theres no difference in the hourly rate.

It's pretty simple:

Hand/hour * winrate/hand * = winrate/hour

If hands/hour doubles and winrate/hand is cut in half then we get the same result. So you need to be able to play twice as many tables without cutting your winrate in half.