I would start by deselecting Network aircraft processing - untick the 'Process Hardware flights' box at the bottom of the Network list. Then experiment with local MyFlights traffic and the settings in the 3D Preferences. Try Min/Med/Max, try reducing the Default number of trail points to zero, increase the Hardware Detected 3D refresh rate from 10 to 20.
If your 3 D view in the Google Earth window is still struggling, then it's more likely to be your PC rather than the RB software. I'm assuming you have a good broadband connection and the latest drivers for your graphics card?
Once you have a nice smooth display using local traffic only, then you can add Network traffic and experiment with those settings. I've got an old (5 yrs?) PC and I'm fine with local traffic, but the PC struggles if I try to ren Network at Maximum to get the 3D models.