These are very different grip options. Measuring grips is difficult because of their irregular shape, particularly the E2s.
E2s are designed to give smaller hands better trigger reach, and this is done by slimming the upper portion of the grip. The actual grip size in the palm area of your hand isn't very different.
The big difference is how these 2 grip options feel. E2s are VERY grippy. Sure they grip well in your hand, but also grip your shirt, your undershirt, and everything else they contact.
Aluminum grips look great, I have then on my GI guns - Mk25 & M11-A1. Their checker texturing feels pretty grippy, without be too aggressive. The knock on 'em is they're cold in the winter, and their black finish knicks easily. So, wouldn't suggest aluminum grips on a carry weapon.
Cheers