Geez, what are you running on those things, that's a 1/2 volt drop! So far with the Vgo 650, I've measured V droop with a Cool Cart (~3.3 Ohm) -.21, CE2r4 metal case (~3.1) -.23, Kanger XL horizontal coil (~2.8?) -.27 and Wow cart (~2.4Ohm) is -.30. All carts were filled.
From 4.25 down to 4.0...