I bought the same unit except I still have the 500GB 7200RPM HDD and single channel 8GB of RAM of the base configuration. However, I changed the wifi card for a cheaper one (Realtek instead of Intel) but upgraded CPU from i7-4710HQ to i7-4720HQ.
When prices drops and I have more money, I will put in 32GB of RAM and a fast SSD. Right now, even without those, I'm still so pleased with this laptop. It's my first computer geared toward performance that isn't a desktop and I must say that it's offering me best of both worlds. Raw performance across all aspects and acceptable portability(it ain't an ultrabook but it's no 2" thick laptop either).
Being an embedded firmware developer for interconnected communication systems, it's really nice to have your main dev machine portable. When I'm at my desk, I can plug in 2 extra monitors (up to 3 on this baby).
I too plan on keeping this machine for a long time. Of course, being a "slim" laptop makes it impossible to upgrade core components such as CPU and GPU but 4 SODIMM slots with 2133MHZ speed capable (prema-mod BIOS required I think) and the possibility of 2*2.5" HDDs + 2*M.2 SSDs(one of them is PCIE 2x too) is uncommon for laptops but very welcome. RAID setup using multiple HDDs/SSDs is possible on this machine.