That's a good question as I'm still learning. My feet are slim, low instep.
EG Nevis 606 UK9D - length fine, D still too high in forefoot. Need a insole/sockliner or C next time.
EG Galways 82 UK9D - pretty good fit.
EG Alderleys 202 UK9D - same as Nevis.
I tried all these in UK8.5E as well and they were too short.
GG Isham MH71 UK9E - too long, wide/high.
GG Canterburies GG06 UK8.5E - perfect snug but comfy fit. Would try same size for MH71 next time.
Conclusion: EGs are shorter but wider in fit than same sized GGs for me.
It is when you cross your legs casually and the sole can be seen. (#dressboot)