Unfortunately, there’s not going to be a way to force the DisplayLink adapter to any higher refresh rates than what the monitor offers in it’s EDID.
Here’s what’s happening: there’s kind of a philosophical difference between what your main GPU’s driver is doing and what DisplayLink driver is doing.
The main GPU driver is offering modes/refresh rates that are beyond what the monitor specifically advertises. These may work (they’re likely based on standard VESA timings), but it’s a kind of “buyer beware” thing – for example, you may notice when connected to your laptop VGA that you can set higher refresh rates like 120, but you may notice the picture isn’t properly centered, etc. for the monitor. That’s because it’s not the native timing recommended by the monitor. It’s probably also possible to set modes that come up completely out of sync.
Rather, DisplayLink drivers philosophically stick to what the monitor advertises for its preferred timings in its EDID - it uses exactly those timings. So it should come up good every time on the monitor, without adjustment.
But if the monitor doesn’t explicitly offer alternatives modes/refresh rates in its EDID, DisplayLink won’t add them to Windows’ list of choices. Thus the difference you’re seeing in terms of refresh rates offered.
So, sorry, this is an intentional design decision/tradeoff of the DisplayLink drivers – one that simplifies things and avoids trouble for many users, but limits what power users could do in terms of overriding defaults.
Wikipedia has good gory details on EDID if you want to read more: http://en.wikipedia.org/wiki/Extended…
Also note that LCDs don’t have the issues CRTs used to in terms of refresh rate and visible flicker. It’s nice to put old monitors to use, though.
Hope that helps to at least explain what’s going on, sorry we don’t have a happier answer. Let us know if we can do anything for you.