Textkit Greek and Latin Forums

As part of catching up with my negelected studies, I have been doing the English to Latin exercises from Wheelock, and I have a question. Those familiar with the film 'Jaws', might now like to start humming the 'daa dum' theme.

They are going to Rome to talk about conquering the Greeks.

I tried a number of ways of translating this, and would like someone to check my work please. (The first one is in the key, so I know that it's right!)

as a purpose clause-
Romam eunt ut loquantur de vincendis Graecis.
as an accusative gerund-
Romam eunt ad loquendum de vincendis Graecis.
because ire is a verb of motion, we can use a supine-
Romam eunt locutum de vincendis Graecis.
and finally genitive + causa-
Romam eunt loquendi causa de vincendis Graecis.
???

What, no-one? Is it that you are still rolling about on the floor laughing at my attempts, or are they (Shock! Horror!) right, and need no comment?

I think the one in the key is the least pleasant of all of those