Preservation fund

I have money in a preservation fund.

The rules are such that I am allowed only one withdrawal.
I can withdraw a portion or the entire amount at once.

If I choose to withdraw a portion, the rest of the money will only be accessible to me on retirement age or to my estate on my demise.
Also the money is fully taxable as per RSA tax legislation, which means if I decide to withdraw the entire amount at once I will be paying tax which will substantially decrease the net amount that I will receive?