How does one mention “first class honors” and GPA correctly on a résumé?

Your first suggestion, Graduated with First Class Honors and a GPA of X, not only seems legit (as another user said); it is absolutely correct.

There are a few different ways to format education on a resume, and in part it depends on how much you have or want to list.

Honors can also be listed as:

• Cum Laude: with honor
• Magna Cum Laude: with great honor
• Summa Cum Laude: with highest honor

1

University -- Campus, City
Degree name (cum laude), month year -- other awards, GPA: x.x _1.

2

List the honors separately:

HONORS

List item 1 years
List item 2 years _2.

3

Bachelor of XX, Major month year
Minor: minor
University, campus, city
GPA x.x, Cum Laude Honors

4

The Harvard Law School Advises:

You should include two separate subsections for each educational degree: "Honors" and "Activities." _3.

UNIVERSITY
Degree XX with Honors in XYZ and ZYX, month year
Honours: details here

Activities: details here

References:

1. Put Your Education to Work on Your Resume
   By Kim Isaacs, Monster Resume Expert

2. Format: Résumé Honors / Awards

3. Resume Layout Guidance
   Harvard Law School

Your first construction seems legit. You can add: Graduated with.....and an overall GPA of X.

You might also put it like this:

Awarded First-class Honours(or Honors) for an overall GPA of X.

Cheers

Edit: and its First-class(http://en.wikipedia.org/wiki/First_Class_Honours#First-class_honours)