In the roughest of terms, the 3.0 has 20% more displacement than a 2.5. Assuming that it can use 20% more air, the math would be simple. A throttle body with 20% more area would be between 65 and 66 mm.
With a hotter cam, head porting, larger exhaust, and no restriction from the MAF, a larger throttle body may be more optimal.
With stock exhaust, milder cams, etc, a smaller throttle body may be optimal.
Other factors may also change the results.
As I started to say, in the simplest of terms, a 65 mm throttle body would be a good place to start with a 3.0 with SVT cams. With Escape cams, the 60 mm would be a good palce to start.
You would need a set of cams hotter than the SVT cams to even thk about a 70 mm throttle body.
My $.02.
