Paypal FX conversion rate, yay or nay?

I couldn’t find any concrete information on the web, especially in the Singapore context, so I decided to do my own research instead. And the answer is? It depends on which credit card you are using.
My total amount payable was US$311.04.
Paypal’s conversion
Credit/Debit Card : MasterCard XXXX-XXXX-XXXX-5230 $448.50 SGD
PayPal Conversion Rate as of Aug. 20, 2008: [...]