Search works fine for me in Spark 2.7.5 (Openfire 4.0.1). Either on Windows 7 or Windows 10. Make sure you have Search installed on Openfire. If not, install it. If it is not available on the plugins list, download it manually from Ignite Realtime: Openfire Plugins and install via Upload menu.
I can’t test file transfers in a real environment. Don’t have Windows 10 machines. In virtual environment both Win7 and Windows 10 get around 1.2 MB/s speed of receiving a file (from physical Windows 7). Virtual WinXP machine gets a considerably higher speed, but it uses different virtual network adapter. So this might be the cause of different speeds. I will try to test this next week in our network (with Windows 7 only).
Do you have Proxy service enabled in Admin Console > Server Settings > File Transfer Settings? I have this disabled, so my clients are doing file transfers directly (the quickest way).