FT2232H bit bang mode maximum reliable data rate?

I have been experimenting on a wireless infrared communication on FT2232H mini module with Asynchronous bit bang mode. Since I only need 1 pin per input and output, I setup both output and input on the same channel (Channel A). I basically connect the output pin to an infrared transmitter circuit and the input pin to the receiver circuit. During my experiment, I found out that my whole setup cannot go any higher than 40Kbaud (about 100 Kbit/s) without generating significant bit errors. I believe that my transmitter/receiver circuit component isn't capable of responding to fast transmission rate (op amp slew rate, etc.).

However, when I revise the whole setup, I found out that connecting a wired loopback (output pin back to input pin) still produce bit errors at about 100Kbaud (about 300 Kbit/s). I have tried to switch around the loopback wire, in case the problem lies with the wire connection, but to no avail. Therefore, I started to doubt if FT2232H asynchronous bit bang mode is capable of delivering high speed reliable read/write function.

There is another issue on FT2232 that really troubled me. The FTDI documentation (here) states the clock for Asynchronious bit bang is 16 times the baud rate. However, I measure the output frequency with oscilloscope and found out that the result frequency is only about 2.5 times the baud rate we set. I am not sure if I understand the whole scheme of bit bang mode correctly, or does the behavior of device changed if I use the same channel as both input and output?

Thanks in advance.

Should be discussed with meaningful code examples.

I didn't use bit-bang mode with high-speed chips yet, but generally, I would assume that the timing is accurate within a single bit-bang sequence packet send to the controller.