"For me, this is one of those instances where being slow to sell...

"For me, this is one of those instances where being slow to sell has been a good thing. My residual holding is now well in the black again. The question is what to do now."

As is always the case, I think any investment decision - to buy, sell or do nothing - is best informed, not by being in the red or the black (which induce human emotions into the investment decision), but by cold, hard valuation metrics (which remove the human emotional elements).

Ergo, the best way to answer your "what to do now" question is to ask yourself:

1. On what sort of valuation multiples should a company like this (given its financial pedigree, growth, management, industry positioning, etc.) trade"

2. On what valuation multiples is the stock actually trading?

If the figures from Point 1 are greater than those from Point 2, then DON'T SELL.
Conversely, if Point 2 figures exceed Point 1 numbers, then SELL.