I would love to delve further into FRV if it had what I mention....
I know its tough, I have used many browsers. Everyone has something they are used to and have to have some feature.
I have liked ACDSEE for its capabilities and speed, but it is not so stable. You are forced to upgrade for stability rather then them patching things with OS updates. So I stopped using it for the most part. LR is too big of a snowball to be fast for viewing alone.
I have also used IDImager/Supreme, which is very nice too, but I don't use it as its as complex as LR, so I just stick with LR. I have used PhotoMechanic, which was missing something a few years back. Owner said they would add it when possible, but I guess it took too long as I don't use it.
I used PhaseOne Media, and the former Expressions Media. Before Phase too over it was actually pretty nice. Now is clunky and broken or simply ilogical layout ruined it. File format issues, etc.
At some point and time, I have tried these, (I found for the price and features ACDSee to be my choice, but it can't support MF digital back files like IIQ, so the stability and the format issue is are the biggest issues.)
FastStone (not for large amount of files), file formats issue
Breezebrowser, also stumbles with large volume, file formats issue.
....One key feature, I as well as many like having is the ability to see and size "filmstrip"/thumbs. (ACDsee does this well with very customizable interface.
This is vital particularly shooting the same subject in very small incremental changes, say a model that is in the pose but makes small adjustments within it. You need to see the group of images in the thumb size large enough to make a decision if #1 vs #4 is the preferred image. So if I have !1 large, I need to see #s2-6 maybe in a large enough filmstrip size to make the comaparison. I can check sharpness individually, but not the overall completion of the shot(pose, eyes, smile, hand, angle, tilt, hair position, clothes, flash output consistency, background). Most of these variables can be confirmed with a good size thumbnail. Why dual/large screen is almost necessary.
Happy New Year!