Just a quick update. As you may recall, I found that using a USB on my Dell E4310 meant the speed of the other USB socket was impacted. In fact, when a GPS dongle was being used to set system time, it meant the error could jump from 2-3 ms to 20ms.
To try to overcome this, it was suggested I try an Expresscard based USB port. I bought a Startech dual USB2 port card, but had to return it as it wasnt recognised on Win7 – even after 30 minutes with one of their helpful online advisors. So I tried instead a CSL dual USB3 socket Expresscard for £10. After loading the drivers that was immediately recognised. It works fine with all the USB kit I tried. So I connected the GPS dongle up to that, hung a Paramount MEII tracking a satellite (22Hz tracking speed updates) on one of the laptop USBs and a Starlight 694 taking very short exposures on the other. Result can be seen above. For long periods the error was 2-3ms with occasional wandering to 4ms. Really not bad at all – plugging into the main bus made a big difference. Well worth the small installation effort.
So, if timing is crucial to you, get a standalone network enabled time source and set up your own NTP server. But if 2-3ms accuracy is good enough, £20 for a GPS dongle and a CSL card will do the business.