How much line till respool?

[faker]

So on my spheros 5000 sw I can fit around 275m of  pe 2.5 line 

And on daiwa freams 6000D 300m of pe 3. Both Used for rock fishing.

How much of it remaining should I consider respooling?

[Steve0]

For practicality, minimal line would probably be enough to afford a strong run plus a bad wind knot. 

Tossing bait, minimal line is probably enough. Distance casting, you'd want your spool fuller (near empty spools generate more line friction across the spool lip).

 

[Rob81]

You could also top fill with mono and reverse the line. That way you have a full spool to allow for better casting but also you're using the fresher braid that was deep inside.

[lhan]

For  shorejigging generally 100m of line is always out for sure, and I would have another 100m saved for any kind of big catch or loss of lines at least.

150m of good braid and some backings can also do most of the time for boni/tailor/rats imo. Not many of them could take 50m of lines even on 3kg drag