Yeah, I'd be curious to know what your results are like using a custom YOLOv5 model. If things are still slow, the issue might be in your quantization process. However if it speeds up, it may just be that the model architecture is too big.
I have it on my to-do list at some point in the next few weeks to add YOLOv8 to our list of default models so when/if I do that I'll keep you posted with the results of that as well.
Keep me posted on how I can be of assistance!