Im in Dallas, TX.. One of the areas that is getting 20+20 or 2x20 LTE first.
While i have no doubt my speeds are attributed to their new LTE im not sure its 2x10 or 2x20
Basically 10+10 / 2x10 has a max speed of 75megs. 20+20 / 2x20 has a max speed of 150 megs.
This was taken from another forum.
"LTE has about 37.5 Mbps of capacity per 5 MHz FD channel (if you're talking about theoretical maximums like you do with H+), so 10x10 is 75 Mbps and 20x20 is 150. Now it's incredibly rare to see those kinds of speeds in practice because they require perfect RF conditions with no one else on the tower, but that's the theoretical capacity anyway...and that's why LTE is better than H+.
As for 20x20 being X times faster, it's hard to say. One disadvantage of wider channel sizes is that your phone is probably spreading the same output power over a wider bandwidth, decreasing outbound signal strength. This leads to a less-than-double performance gain in all-else-euqal non-ideal conditions.
However you also need to factor in that, above a certain speed, data usage doesn't really increase, and the speed you're getting is some function of the free capacity on the cell. So if you add 75 Mbps of capacity to a cell, with 45 Mbps of that readily available under normal circumstances, and people only use another 15 Mbps of capacity due to the faster speeds, you're looking at average speeds 30 Mbps faster than you were before!"
Faster T-Mobile LTE Arrives in Dallas | DSLReports, ISP Information
I for one am happy to get faster speeds but what makes me the happiest is as the system gets more crowded it will be able to keep up with the additional users and not get bogged down. Given the backhaul is in place at the tower, which so far it seems to be.