you have passed the RT limit of your system and not the IoHD
“If you’d rather lower the playback quality of your video to increase the number of real-
time effects that can be played back, you can select the Unlimited RT mode. In this
mode, Final Cut Pro attempts to play as many frames as possible, even when the effects
in your sequence exceed the processing power of your computer. Real-time effects that
can play back without dropping frames still appear with green, dark green, or yellow
render bars as appropriate. However, when the number of effects exceed your
computer’s processing power, an orange render bar appears, indicating that real-time
playback will occur, but that frames might be dropped during playback in this part of
your sequence.”
One way to get great TC burns is to turn it on with the AJA control panel. The down side it the TC is from the timeline but if you match the TC of the timeline to the clip you get what you need. I think you maybe able to get the clips TC if you play out of the AJA TV.