I find these contradictory and mutually exclusive. Having the proper
bankroll involves assuming that you'll play the proposed game forever.
Quitting while ahead may feel good, but I've asked several people who
advocate it what the financial benefit is of extending the time
between a winning play and the next play and have yet to get a
coherent answer.
"Proper" bankroll really assumes that you'll see something close to ER and
so have enough to weather expected variance. It's not a safe assumption
though, since most play is short term and ER doesn't apply on a per session
basis.
Quitting while ahead is always a good idea, but obviously quitting at, say,
plus $5 and then waiting an hour or so before the next session is purely
arbitrary and doesn't make a whole lot of sense. What does make sense is
setting realistic win and loss limits. By win limit, I mean a fall-back
limit. If you're $200 ahead and things start turning, you decide to fall
back no further than, say, $150, just as an example.