I am currently working with UE4 only on laptop and my configuration is quite similar to the one you are mentioning: same proc, same graphic card. I have 16Go of Ram though, which makes things more comfortable with other greedy apps opened. Everything works really well, even in VR.
My computer is an XMG assembled by a German company named MySN (http://www.mysn.eu/). They offer flexible configurations with very high quality components, a good warranty and a good support.
At the time I bough it I also looked at Lenovo because my previous computer was an IBM and I was really really happy with it. I don’t know if Lenovo still offers the same quality and on-site support though. What I know is Lenovo is quite expansive compared to some other big configurations as XMG or MSI.