Why is the data transfer speed not faster?

According to the official USB-standards it is not allowed to transer data via USB full speed if the physical connection is using unshielded wires. The black and yellow transfer wires are unshielded. We needed to use those wires because we would not have been able to route them through the cut-outs of the casing if they were shielded/too thick. This is the reason why we have to transfer with low speed.

Is it possible to transfer data to the X-B.I.T without installing it into the XBox?

Yes it is. You need to connect the external board with the internal board with yellow and black wires (ensure that the write-protect seal is removed). Connect the USB-Cable to the external board and the PC and start the software. You can now write a bios to the X-B.I.T flash. It is recommended to do that before you install the chip into your console to test the functionality of the flash feature. If the USB flash feature doesn't work after installing the chip into the console it is very likely that installation is wrong.