The Logitech G5 appears to be an MX518 with 400/1200/2000DPI adjustable resolution and laser instead of LED tracking. It's priced at 59EUR. The G7 is a cordless version of the G5 and retails for 79EUR.
Then there's also the MX610 which looks like a cordless version of the MX510 with laser tracking, a new design and a 49EUR pricetag.

The MX610

The G5, it looks like you will be able to make the mouse heavier with some small external weights.

The G7