Hi autopilot, a great question.

Anything that improves your transciever's ability to communicate with the surrounding cells is going to be a good thing. But as others have said, it will not improve speed per se, particularly given that you have an HSPA+ device communicating with what sounds like a regular HSPA transmitter mast. However, when the mast is updated to HSPA+ then you will see the higher speeds and performance. And again, with a more capable arial you will benefit from stability and availability over and above that which the stock device can achieve.