I can confirm it will most likely be
LESS than 3Mbps. While I didn't run any speed tests that last time I was in Yosemite Valley (March 2013), I got the best performance (less webpage lag, more responsive iPhone apps performance, faster photo uploads) on Yosemite Lodge's WiFi network than on AT&T's 4G network (and every time in the past I've run a speed test on the Yosemite Lodge WiFi network, I got results usually ranging from 250Kbps to as high as 900Kbps).
If you ever tried to use AT&T 4G network in the Bay Area, you'll note that it can get capacity constrained anywhere where there's a crowd of people. Even in March (when Yosemite Village wasn't that crowded), I got only so-so data network performance trying to run iPhone apps (like the Facebook app) using my iPhone 4s on AT&T 4G network. Yosemite Village will be far more crowded in June so I wouldn't be confident that you could get consistent speeds of 3Mbps (or more) as you seek. The performance of AT&T 4G network did improve at night (when there were far less people inside Yosemite Valley than during the day).
But I'm wondering why do you need such a fast data network connection for your work?
For most of my work needs, including downloading PDF files, connecting thru VPN to the company's internal network, and administering Unix servers and Oracle databases, even a consistent data network speed of only 300Kbps is usually sufficient.
Do you need a lot more bandwidth for video conferencing or cloud apps?
At home, I want a much faster data network connection simply because I stream a lot more video than I do while at work and also because it improves the call quality of my VOIP phones.
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