you know that a tiny drop of oil placed on the rails will keep the things lubricated for about 6 months ?
A reservoir in a bearing is just asking for leaks.

I have no idea what make the rails are on the sapphire - but they're all you actually need :-)

I was hoping the whole: 'my slow printspeed is 250mms and my fast is 500mms' might have inspired you to actually consider USING your printer, at some point ;-)