This version of the bootloader works on both 1k and 2k page size devices and on any flash size. The address of the pindef structure is fixed to the 3rd-to last 1k block. That is 0x801F400 on 128k flashes or 0x800F400 on 64k.
You do not need to upgrade your boot loader from V4 if you are on a 128k flash size, 1k page size device like the STM32F103RBT6.