First, the T4500 mobile CPU is the top of the line in that series. The T4000 series is the best of the T series. Beyond that it will take some research to see if there are any processors that will even work in the CPU socket in your laptop.
But things are not that simple, as the BIOS must support the CPU, and you cannot assume that it will support all CPUs, it more than likely will not. Laptops are really not made for changing CPUs like desktop PCs are, and frankly I would not recommend it.
Your best source of information will be HP about this, since Intel does not have information on laptop boards on their web site, since they are very likely made just for HP.