Cash Out Refinance for student loans?

[Sam White]

Should I cash out equity in one of my rentals to pay student loans?

2 years ago I bought a duplex for $123,00.  Current mortgage is $110k @ 4.2% interest. 

Current price is about $200k for Market comparables for 2 exactly the same on my street.  

I have about $23k left on my student loans. Would it be wise to ReFi my duplex at 75% LTV?

Making the mortgage $150K and pulling out about $40k in equity.

Rent roll is: Unit A - $850, Unit B: $600 = $1450/monthly

Current PITI payment is about $940

Part of me wants to keep the mortgage payment low and work to up the rents, therefore increasing the spread of my cash flow.  Other part of me wonders if I should cash out ReFi and become debt free (minus all mortgages I hold on rentals). 

Thoughts?  Anyone make the decision to do this recently?