kypa

Don't agree here: https://forum.armbian.com/index.php?/topic/1925-some-storage-benchmarks-on-sbcs/&do=findComment&comment=14802 (though: you get what you pay for, ODROID-C2 eMMC with larger sizes is pretty expensive)
 
As for the other requests: 'browse facebooks or download movies'... no idea whether that's on some SBC platforms ok-ish (I would not even try it) and regarding Java I've to admit that I learned to hate Java applications already 20 years ago too much (we had a Sun Enterprise 450 back then with just 256 MB RAM and a shitty Java application that needed +1 GB after a few hours swapping the machine to death)
 
 

All socks have terrible slow filesystems even 10 years old market pc runs faster.
Example linux swap is terrible slow from sd-card.
javas biggest problem is and has always been garbage collector it makes the software really cpu depended and on weak systems the performance is poor. 
 
For a pure performance I would go for the small size embedded pc's.
Java is reasonable if you have alot of memory, strong CPU and the application loads as match as possible at startup.