If you've been through the Cheat Engine tutorials, it's much better to scan for the memory address that contains your speed value and modify it directly.
Speed is a FLOAT value.
- The default run speed is 9.1875.
- The default walk speed is 2.5.
The key binding to toggle walk/run is not defined in GW2 until you set it. (go into the options) This will allow you to easily scan for a known value you can control and find the address for your speed.
You should use Cheat Engine to pointer scan for the speed address found and add a good pointer to it. (Lots of guidance on the CE forums.)
I haven't observed any noticeable rubber-banding using this method, but then I don't crank my speed more than 25% above whatever my current unmodified value is.