$65bn is 18% of Greece's 2008 GDP. At 5.33%, servicing the debt will consume 1% of Greece's GDP and require a roll-over of the debt when the debt expires.

The roll-over is more problematic than the actual interest payments.

What this does is set a cap on the interest rate that Greece has to pay for up to $65bn of its debt. As you point out, the latest auction in the open market was oversubscribed at effectively a lower rate (given the longer maturity). Greece may still manage to auction its debt at a lower rate than the one offered by the EU/IMF and only turn to the EU/IMF for any unsubscribed debt. As somebody quoted in the comments, the loan "may not come to pass" and that would be a good thing because it would mean that Greek debt would be priced at a lower yield than this 5.33%.

The brainless should not be in banking -- Willem Buiter