The 1D Mark III and IV both have an on/off switch for the portrait grip and I find it valuable. I carry my rigs inverted using Sypder Holsters and being able to turn the portrait grip on and off prevents me from taking inadvertent hip shots!Would you consider getting a second 5D3 instead of the 1DX you have on pre-order?
Hip shots with the 5D3 & Spider Pro? I have the twin holster belt. With the 5D3 & BG-E11 on the left the shutter gets bumped constantly. Shifted to the right the release is on the outside, so no hip shots. Switching it off can mean missed shots if you reach quickly for the camera, go to shoot vertical & there's no action. Damn! Missed the shot! I have a 1D4 on the left holster and the button is just positioned differently enough not to trigger every time you take a step.
Here's my BG-E11 mini review. It's big.
With the grip attached the 5D3 is taller, thicker and around 30 grams heavier than a 1D Mk4. The 1D Mk4 with battery is 1375 grams and the 5D Mk3 with BG-E11 & two batteries is a beefy 1406 grams. I used to pack the old 5D as a lighter weight option. I'm surprised. After shooting with both cameras, the Mk4 feels compact by comparison. I have used 1-Series bodies or added grips to APS-C and 5D bodies since the beginning of time. The 5D3 with BG-E11 has the disconcerting characteristic of the rear quick control dial being a noticeably further from your thumb in portrait mode than in landscape mode. I can't reach it without altering my grip. This is an ergonomic negative. But I'll get used to it.
It's an ergonomic positive though to have the joystick right there on the grip. It quickly becomes easy to find, making focus point selection quick & simple. Now if only we could see the black focus points! (see black focus points thread)
Will I cancel my 1DX pre-order? Almost certainly. A BG-E11 on the 5D3 makes for a very strong workable package that is not prefect, but what is? It's a far more significant upgrade over the 5DII than many people give it credit for. I give it an 8.5/10