We are upgrading from 5.5 EP to either V 6.0 or 6.5

We are planning on upgrading our GW system from 5.5 EP to either 6.0
or 6.5
this weekend.

We know that we can upgrade to 6.0 and continue to use the 5.5 clientagainst the 6.0 PO's with no problems so we can upgrade the users as

But, since we also recived 6.5 (due to upgrade insurance) I don't want
have to go through another upgrade process again if I don't have to.

So I have a some questions:

1) Is there any advantage to first upgrade to 6.0 then to 6.5?

2) Can I continue to use the 5.5 EP client againt the 6.5 PO so I can
the client upgrade process according to my timetable.

Thank You