Oh - if you are using a subframe on the guide camera, the overhead should be small. FWIW, I use StarTech industrial USB 2 hub. It works very well indeed and uses the NEC chipset I believe. My friends had issues with various other hubs and when I lent them my spare, their problems went away. They are expensive but usefully run off 12Volts, making them easy to integrate into the scheme of things. My 7-way hub is handling the mount, QSI camera, guider, focuser, power control system, observatory controller, cloud detector, weather stick and all-sky camera.