I'm upgrading to the 830 from a 920, mainly because my 920 has been having serious issues (and was rendered useless today as it now won't connect to any cell towers). I won't gain much by moving to the 830, but I won't loose much, either.
The 830 is very similar to the 925, inside and out. Performance could be a little faster because the 830 has a newer quad core processor, but the clock speed is actually slower, so this isn't necessarily true. One improvement is that the camera launches faster, and after Lumia Camera is released, it'll be even faster. Screen tech is different (IPS LCD instead of the 925's OLED), you get a bigger screen (at the expense of pixel density), slightly (SLIGHTLY) better camera, SD card slot, in-built wireless charging, and sensor core for pedometer n stuff. And a free Fitbit if you buy it from AT&T. (I think they're still doing that deal, anyways.)
You said "newer upper scale..." The 830 is definitely newer, but hardly upper scale. It's roughly the same. If you like your 925, you'll like the 830, but then you might wait for something new coming in 2015. This could be quite a wait; no one outside Redmond knows. Also, you could look at the M8 for Windows for "upper scale." It has significantly higher specs, but keep in mind that WP runs smooth on just about anything, especially including the 830. If you want to stick with Nokia/MSFT Mobile and don't mind the size (everyone seems to say you get used to it eventually), the 1520 is another option. It is similar to the M8 in specs, but it'll start showing its age soon. It isn't really a new phone.
I say just watch a couple reviews on youtube and go into the store to play with them yourself.