Hi Randy,
I just used a Sony UBP-X800 as part of a 4k video upgrade to a 15 year old dedicated home theater for one of my clients. It replaced a OPPO BDP-95 pre-4k player. If all you care about is a good 4k UHD video signal out the HDMI the Sony is fine. If pride of ownership based on heavy duty construction, more metal and less plastic get an OPPO now while you can. The UBP-X800 strikes me as intended to mostly stream content and occasionally play a physical disk. If you intend to invest in or already own a collection of DVDs, BDs, and 4k UHDBDs the considerably more substantial transport OPPO uses would tip me in its favor. I expect my client to stream 90% of the time so for them UBP-X800 is fine.
And in case anyone is wondering the projector used in this upgrade is the Sony VPL-VW285ES 4K UHD and it is stunning.