Because the G5/6 blades have a longer cutting edge and the fusion treatment that does help them stay sharp longer, and unless you can see all the specs for your particular model number of G3 and make sure they have the same lift as the G5 blades, you may end up disappointed with them. I bought mine because I knew the set I needed for sure had as much lift and they don't make a G5 for that particular machine due to its age.Forest Depot has G3 and G5 for literally pennies more, what did you recommend G5? I will weigh my factory high lift mower blades and see what they weigh for comparison. However, I do not see a weight listed for these blades on Forest Depot.
Almost all riders use blades that are .203" - 205" thick, or heavier like mine at .250". The only added weight would come from the G5 being a half inch wider, which would only add a few ounces per blade, and with the serrated sails, shouldn't make the machine work any harder unless they have much more lift than your oem blades.