Hmm never heard of Signal degradation. But why are you using the Laptops VGA output anyway? All the outputs are hardwired to the internal resources, if you want to connect multiple displays with your ultrabay adaptor correctly make sure all the connections go into your external gpu.
If someone is looking for an extender prepare to use your right to return, because length and build quality determine wether your card will work well or not.
A 1080 should work fine with pcie 3.0 8x, a TI might begin to loose a bit performance, but that effect might be negligible most of the time and only relevant in some scenarios which need faster pcie speed.
In my case with the gtx 980 which is quite equivalent to a 1060, I do not loose any performance whatsoever, the only factor in determining gaming speed here is the -compared to desktop setup framerates- slower CPU.
I run at 2.4 ghz most of the games (its a 4900 MQ for 8 MB of cache inside) and its stays below 80. With 2.8 ghz (which is stock speed/throttle target) it rallies at 80 and without changing anything about airflow i can manage to keep 3 ghz without throttling (happens when the cpu hits 90).
Any more speed would need an upgrade of the cooling solution, 3.2 ghz might be manageable with certain games but not all.