Yo! Good question!
First question, IMHO, is your long term goal. FICO scoring is not the same financial planning.
Your stock assets, just as bank accounts, IRAs, etc, do not enter into FICO scoring. Father FairIssac does not care about them in your FICO scoring. So if you take assets not scored by FICO and apply them to FICO-scored debt, such as reported installment or revolving credit TLS, you will definately get a FICO score boost
But FICO score is not the begin or end all in financial planning or in credit decision making. If you plan to apply for additional credit in the near future, your creditor may look not only at your FICO score, but at your ratio of debts to assets, and your assets will drop if you cash the stock.
No simple answer, good buddy, unless you are looking only for a FICO boost.