I’ve posted number of posts about the G2 and the Index (I own both). I’ve lately posted the following in a private discussion which might help you too:
As for the Index honestly it has less resolutions than the G2 and it shows, for sure, but mostly in flight simulation. Playing other games like HLA, Pavlov, Onward, and many others, I never felt it lacking pixels at all (maybe you get the edge in Pavlov when aiming at the distance with a G2 though). The most striking difference to me is immersion and completeness. In short: you don’t feel like something is lacking. It is a well rounded and complete VR experience in every way, with stellar tracking, unbeatable controllers (for anything other than flight simulation it matters), and so much tweaking and low level configurations. I don’t even need a controller to change SteamVR settings on the fly because there is a controller button right on the headset itself, working as a point and click interface! It is very handy to quickly disable/enable motion smoothing live (no need to exit VR…), to change fixed frame rate on demanding sceneries while still flying, etc… (I’m playing the salesman here!)
So resolution is indeed lower and to give you an idea what it looks like, set your G2 OXR to 45% and TAA 100. This is what I see in the Index roughly. For example in the TBM I can read the ITT green numbers from the normal seated position, but this is at the limit between reading and decoding number shapes. Please note this is what I see (OXR 45 on G2 vs SS 124 on Index) but you’ll see this at a small center region only in the G2, while I see this level of detail roughly +80% of the view left from right and top to bottom… (vs 15% on the G2 for me).
Beyond the mere resolution though, you get larger horizontal FOV and even more vertical FOV than the G2, with smaller black sides between your temporal region and the LCD panel making it less a goggle you see through and more an immersive be there experience.
The Index has more glare though and some are not fond of this. I didn’t until I set my mind as if I’m being blind folder by the sun and that’s it (like IRL nowadays at my ‘old’ age where a bright screen in a dark room is sensibly less bearable than when I was younger 
)
There is one thing I don’t like with the Index in FS2020 compared to the G2, and this is the color gamut*. Both panels are sRGB with about the same coverage on paper, but the Index is white clipping a little more, enough to see the difference. Otherwise the luminosity is about the same between the G2 and the Index when set at 130% (the default - yes you can also adjust this in the Index along with RGB gains), but when you set the Index at 160% and look at the sun in FS2020, or have a bloom effect on a mirror surface, it is so life like you blink the eyes!
Here is one of my post comparing the Index and the G2 in practice with an aircraft cockpit for reference (about the edge to edge clarity) which also contains other useful info:
Reverb G2 Sweet Spot Discovery - #41 by CptLucky8
Otherwise I’ve done a few flights lately over UK aboard the WT CJ4 (first time using the WT version). It was certainly taxing a little more my system as exhibited by more wobbling with motion smoothing. And this is where the Index again is superior: not only the latest SteamVR allows incredible 5 to 1 motion smoothing (15fps → 90Hz for example), but with the headset mounted controller button, it takes a few seconds adjusting this live:
- you notice wobbles
- you press the button and SteamVR overlay displays
- you move the head to point the dot to “Display Settings” and press the button
- you move the head to point the dot on the scroll bar and press the button to scroll down
- you adjust the fixed rate from say 22.5 (my usual value) to 18 (for this test)
- you press the button while looking outside the SteamVR overlay popup
- you’re back in the sim and no more wobbles!
Very handy I can even do this hand flying now without pausing the sim.
This is an example of what I call “immersion and completness” with the Index.
PS: and with the WT CJ4, at TAA 100 + SS 124 the EFIS were super clear and very legible even with the Index. I couldn’t be more happy, really.
*this is why I’ve asked for Asobo to include settings to adjust the color gamut too 
[BUG/FEATURE] Provide a Sharpen strength setting, and more post-processing effect controls in VR