I would not have thought you would notice much difference.
Here is a chart from Intel showing the laptop CPUs, and as you can see they both come from the same family of CPUs (scroll down)
http://www.intel.com/products/processor_number /eng/chart/core2duo.htm
When companies "make" a CPU they dont make a 1.83Ghz one and a 2Ghz one, all they do is make them all the same, and test them at the end.
When they test them they see how fast they will go and whatever speed they reach they are put in that box.
So you will probably find that the T5750 and T5550 were made at the same time on the same production line, and one managed to go a bit faster than the other.
But the extra CPU speed will make little difference in the "real world" where other factors come into play.