The 2 CPUs that I have is the Intel Celeron B830 and the Intel Core i7-2640M. These 2 CPUs have the same socket, generation, model, chipset, TDP, and RAM. Except the only thing different is the steppings.
Intel Celeron B830 Stepping: Q0
Intel Core i7-2640M Stepping: J1
Laptop: Toshiba Satellite C855-S5347
I doubt that stepping matters in this case. Whst you need to do is verify that the BIOS in this laptop has support for the replacement processor. Only Toshiba is going to know this; you need to contact them.