In reply to Kean:
The GRIGRI 2 is optimised for 9.4 mm to 10.3 mm ropes, while the GRIGRI+ is optimised for 8.9 to 10.5mm diameters.
Petzl also say that the GRIGRI 2 'may be used on all 8.9 to 11 mm dynamic single ropes' and 8.5-11mm for the GRIGRI+, in other words you can use a wider range of ropes but they optimise as above.
Suggested retail price for the existing GRIGRI 2 is £60, and the GRIGRI+ will be £85
Post edited at 13:33