If you take size out of the equation, it seems like the 8+ and the new se will perform about the same. Both have 3gb of ram (nearly a guarantee the new se has 3gb). I’d assume the 8+ will get better battery life. Pictures are most likely a wash, with the se possibly having a slight advantage in some areas. The a11 will probably be pretty much on par with the a13 for most usage situations. Obviously the se will score higher on Geekbench, but in actual use I don’t think it’ll be very noticeable.
I’m on the fence about trading in my 8+ for an se, I’m just trying to figure out if it’s an upgrade or a lateral move. Obviously the Xr and above are better overall phones than the new se or 8+, but these are the only 2 I’m comparing.
I wouldn't because it's a compromise in terms of display. Sure for 399$ it's tempting, and i still like the old design with the Touch ID, and you get the A13 Bionic (the A11 is still a fast chipset on iOS 13) and you also get a Portrait Mode upgrade that includes Front Facing Camera Portrait Mode plus Depth Control plus the sixth Portrait Mode effect (High-Key Mono) that was introduced with iOS 13, and also QuickTake and Stereo recording. From the 8 it's an upgrade, but from the 8 Plus it's atleast a downgrade in terms of display. You end up with a smaller screen and you'll lose the 1080p resolution and 3D Touch. I don't know, maybe Haptic Touch is the same experience by now and it's just software-based. That would also work for me. But the bigger screen and the 1080p / 401 ppi is something i value by now.
If you have no problems switching back to a smaller screen, it would make sense to trade it in for the SE. But for most people, they don't wanna compromise on the bigger screen. Myself would like a 256 GB SE Plus, but that would be in the Xr / 11 price range. And for 649$ you can get the Xr/11 no problem. (The 256 GB is already 549$ and the Plus is usually 100$ more). Yet for those who are fine with 64 or 128 GB, i think that a SE Plus would be definitely be an amazing option and cheaper than the Xr / 11.
Also don't forget that the Battery Life on the 8+ is still better than the one of the 8 / SE.