Ok lets go with this, dont really know where to start.
When changing FoV you only change it wide and not hight, hight still the same.
5k+/signal is supposed to be 1440 and 8k 2160.
When setting Pitool to Large FoV and 1.0, I can get close to both headsets resolutions, using SteamVR supersampling slider to 2303x1462 (Similar to 5k+/signal but not the same…) and 3402x2060 (same 8k similar but not match really).
First, are we all displaying image not at the native resolution of the headsets? (Yeah 8k upscaler etc etc but what about the 5k+ in this case?)
Second, why cant we match headsets resolutions?
But thing get much worse now, since the last update of SteamVR :
Before this, every FoV had the same image ratio, much wider than highter even if couldnt match headset resolutions.
As I and some others already said, there was some clarity loss in Normal and Large FoV.
I figured out than with Pitool 1.5 clarity was good even in Normal FoV but when running games with Parallel Projection activated the clarity wasnt THAT good again.
And when checking resolutions in SteamVR, Parallel Projection changed ratio, image was almost square displayed, almost as wide than hight. And performances was less good (if image was calculated that way, lost of wasted calculation).
But now normal FoV without parallel projection is square just like if Parallel Projection was activated and when activating it, it dont change much resolution since its already square! 1728x1462 (for matching 5k+/signal) and
2553x2160 (for 8k)
To sumary :
From Large FoV to Normal FoV = ~-600(~-800 8k) Pixels less in wide for -20° FoV! No wonder why since yesterday I was like “what settings did I ruined to have jagged edges like that?”
I lost clarity since last SteamVR update which was yesterday or something like that, so I checked resolution and found out this.
Seems now only Large Fov can give good clarity (1.25 Pitool to get since resolution more or less fit with the headset. good one but what about the GPU demanding games?)
Just tried Arizona Sunshine after typing all this, with “Signal resolution” 2745x1743 (couldnt go lower with 1.25pitool set) and with “Panel resolution” 3784x2402.
80fps with Signal and 65 with Panel but Iam not sure I noticed a difference…tried several times how clear I was seeing zombies faces far away and was the same or would need a side by side to see difference which mean its not much.
I know I might not be clear in what I say I am sorry. (told you I had a clarity issue 
)