GG is the friction level at ambient and elevated temperatures. See here:
http://www.ducatigarage.netfirms.com/brakepads.html
H is the max, G isnt bad all things considered. I dont know if most OE pads are even 'G' rated... IIRC, most are 'E' or 'F' for ambient and elevated temperatures.
DOT Pad Codes
This two letter edge code mandated by the DOT, and painted on all street legal brake pads, will give you some indication of their ability to resist fade. But only if you know how to read them. However, because of the wide range involved in each letter, it is only a rough indication.
Explanation of D.O.T. Edge Codes Located on all Brake Pads Official D.O.T. Edge Code Coefficient of Friction (C.F.)
@ 250 F and @ 600 F Comments
EE 0.25 to 0.35 both temps 0-25% fade at 600 F possible
FE 0.25 to 0.35 @ 250 F
0.35 to 0.45 @ 600 F 2% to 44% fade at 600 F possible
FF 0.35 to 0.45 both temps 0-22% fade at 600 F possible
GG 0.45 to 0.55 Very Rare
HH 0.55 to 0.65 Carbon/Carbon only.
O.K. up to 3000 F where it glows
Notes: These edge codes are located on the edge of the friction material of every brake pad by government regulation, along with some other codes. The first letter is a grading of the C.F. at 250 F and the second letter is a grading of the material at 600 F. Each letter grade can actually have quite a range of C.F. But a difference in the letter grade from medium to hot temperature could be an indicator of fade. The letters can be in any order. Therefore FE pads fade when hot, and EF pads would not grab when cold.. Also, you should know that Steel on Steel has a C.F. of 0.25!! So EE pads have only marginally more torque than no pads at all! Therefore FF pads are usually considered the minimum for a high-performance pad.