Full Speed Ahead with the Galaxy S 4G on T-Mobile

"T-Mobile currently only has two phones capable of taking advantage of its HSPA+ "4G" network, the myTouch 4G and the G2, but on Thursday the carrier announced the first phone to be able to support the network's theoretical maximum speeds."

It was just announced that the Samsung Galaxy S 4G will be the first phone capable of utilizing the full bandwidth of the T-Mobile HSPA+ 21Mbps network.  No other details were given about the new Galaxy S 4G device.  I would like to know what's different about this phone than the myTouch 4G or the G2 that gives it faster network throughput.  Hopefully all those LTE devices we saw at CES will be capable of utilizing the network bandwidth available to them when they are released.  Has anyone run any bandwidth tests on their myTouch 4G or G2 when in and area with HSPA+ ("4G") coverage?  What download speeds do you see?  Do you notice a big difference when using your device in 3G coverage as opposed to 4G coverage?