dell latitude e5400 upgrade compatiblilty. CPU, WIFI, BT, GPU...etc

I have a dell latitude e5400 win 7 pro and it is getting older. needs a cpu upgrade if possible and I will install a killer wireless n 1103 to use the triple antenna's within the laptop. ( really like that feature).  I have already put a Plextor SSD into it and 4 gb of ddr2 800 MHz ram but I would like to push this computer to its limits since upgrades are cheap now.  I found some reviews that the cpu is available as a t9600 core 2 duo.  im not sure if bios would support this cpu though.  It currently has a p8600 that is for some unknown reason clocked to 2.53 ghz I swear cpuz confirmed it I cant oc this laptop but it seems to do it itself... anyway the t9600 would be a good upgrade for this if it is possible.  does anyone know if it is? also since im upgrading to the killer wireless n that card does not have BT built in.  I am aware that dell has several usb style internal sticks that could work in this laptop. which one would that be so I can get BT back and if there is an option I would like it to be BT4.0.  also is there some options for a faster gpu? im running multi-moniter setup and I seems to tax my gpu a bit hard sometimes. sorry I don't know the gpu off the top of my head but if there were options from the factory that means there are multiple gpu's that I could switch to.  YES I KNOW THE GPU IS SOLDERED TO THE MOBO. but one can buy a new mobo... and finally with the wwan card slot what is the best 4g card out there, not that I want to get one as I wouldn't use it just querious if you know how much they run for.