My Thinkpad still runs Windows 8.1 and to be honest, I'm very satisfied with it. Going to Win10 will make older CPUs feel slower. Win10 also likes to thrash storage a lot due to aggressive caching algorithms. If there is nothing really important that needs Win10, I would suggest to enjoy Windows 8.1.
There are several versions of the P37/W/X, with different BIOS: FAxx, FBxx, FCxx, FDxx. It would seem your model uses the FBxx family BIOS, but that is only a guess. Can you give the full specs of the machine, model and/or part #? Is there an update feature within the UEFI/BIOS and have you tried using it?