Jack - my presets are leveled pretty much the same way the Factory ones are. In facts, i worked with another beta team member on leveling Bank B and C of the firmware 11 Axe-Fx III Factory presets.
The +4 and -10 setting options are to optimize with your playback system. They have NO effect on the tone of the presets. It just determines the output level coming out of the XLRs, think of -10db as "pad." If you are using pro-grade equipment (for example, I am using Universal Audio Apollos and also Atomic NEO CLRs), the +4db setting is recommended -- then you dial the Output 1 to optimize to signal level leaving your unit. I know the +4 db is right for me, because the digital S/PDIF signal matches and if I use -10 I can't get a good, song Axe-Fx or FM3 signal to show up on my console. if using FRFRs, you want to hit them HOT and then use the input knob on the FRFRs (if available to make sure the signal won't clip), then dial the volume on your FRFR Output.
If you are using consumer grade gear or interfaces for your DAW, then the +4db setting can be too hot and that's why the -10 option is there. Two things about this. One, is ideally both the factory presets and my presets should be leaving the outs of the unit at around -12 db (average) as read on a digital mixer. That's good -- it's hot but far enough away from the dreaded "O" zero point at the top if a digital mixer's channel matters where a sound will distort and clip. If this were analog gear using old school VU meters, then for that, their equivalent is the zero mark, and the VU needle will hover around zero a sustained chord, but move into the red from time to time.
Second is that some "pro" gear out there -- the Scarlett Focusrite preamps comes to mind -- has built it and "pre-set" gain added to mic preamps that you cannot dial out!!! People were plugin XLR cables from their Axe-Ax into a Scarlet Focusrite XLR input and complaining "the signal is too hot, it's your presets." No it wasn't. It was the Scarlett adding extra gain to the signal. Once those folks learned can by pass the XLR preamp added gain by using the TRS 1/4" jacks, then all was good and levels were working as expected (another classic example of "gotta read the manual!).
So to summarize, the +4 db and -10db have no effect on the actual tone/sound, just the loudness. But loudness can affect how you hear the sound (Flectcher Munson effect) as well. Hope this helps some?