Movement speed(MVS) will boost everything, if you have good enough gear, elite mobs in f.ex. Act I are just a bump.
If you are farming elites only, there will be a lot of running involved. When I do runs, I'm running like 3/4 of the time.
Consider the math.
Movement speed is capped to 25%, you can get there with 12% on boots (obviously) and then mixing in some legendary armour to boost MVS. Equipment tips in the bottom of this article.
Lets say the run takes 30 mins. With 25% MVS, you can decrease it to:
(3/4 X 30 min) X 0,8* + (1/4 X 30 min) = 25.5 min per run*0,8 is the MVS factor, increasing your MVS by 25%, makes you finish a lap at 80% of the time. That comes to 30 / 25.5 = 1.176, increasing your runs på 17.6%
How does that relate to Magic Find?
Magic find, you can get to 125% very easily, for a total of 200% with Nephalem buffs.
Running 17.6 % faster means you get the equivalent of 200 * 1.176 = 235.2 MF
And it scales very well
With 300% MF at max, you get 300 * 1.176 = 352.8 MF
Conclusion
The higher MF you have the more MVS is worthwhile. MVS at percent by percent starts to outweigh MF at as low levels as 125% MF, also take into consideration the guaranteed rare drops from elite and bosses where you rolled low on MF, you'll get more of those with higher MVS. Also consider that MVS does the exact same thing for Gold Find at the same time. Also consider that Blizzard might nerf MF anytime soon, see Magic Find Gear Swapping
Equipment tips
Don't go for movement speed on weapons, those weapons usually have too poor dps and we need to keep killing fast.
On my build I have 'Inna's glory' pants, with 7% move, 11% MF, a little resist and 140+ vit. Very crappy pants for main build, but excellent for MF build.
For bracers I have 'Lacuni prowlers' woth 6% move, 12% MF, 5% IAS, increased gold pickup. Increased gold pickup is very nice for speeding up runs.
