I have a Nifty mini drive in the card slot for my Photos and iTunes library, with a 128GB card in there, and it works very well, meaning that no more than half my SSD is full at any given moment. SSD: Can be swapped out for larger sizes.It thermal throttles at around 3GHz for heavy tasks like encoding video. But this is still amazing for a four year-old computer. That's from a fourth-gen i7 chip! Yes, these are synthetic benchmarks and admittedly I reapplied the thermal paste, which gives me marginally better performance. Performance: According to Geekbench my MBP is STILL the fifth fastest MacBook Pro, beating even 2017 MBPs.
5K display compatibility: The discrete AMD graphics via Thunderbolt 2 can drive a 5K Dell UP2715K display, or two 4K displays, or just 1080p displays via Displayport.
Standard-sized HDMI out for plugging into just about any TV.