I read a lot about this a few years back, and i came to the conclusion that it's a wash.
The story that the QWERTY layout is designed to slow down typists is a myth - propogated by Dvorak. QWERTY was designed to drastically decrease the rate of jams in mechanical typewriters, and it worked.
The government studies that proved the Dvorak layout is better? Run by (drumroll please) . . . Lt. Dvorak of the US Navy.
The navy does a lot of crazy studies for technologies and techniques that they never use. One of my submarine core friends tells me that they tested the use of negative ion generators in the air filtration systems in submarines once - and found that the seamen were happier, slept better, were more alert at their workstations, and stank less when they got off the boat. And the decision was made to never allow a negative ion generator to be used on a US submarine.
All of the fastest competitive typists in the world use the dvorak layout, but none of them, when asked, attributes their speed to the layout.
My outside guess is that in the time it takes to surpass your QWERTY speed when learning the Dvorak layout, you could surpass your QWERTY speed by a wider margin without learning the Dvorak layout.