John N wrote:
...Will the new D7500 out perform the older D500?
No, it won't.
They have the same 21MP image sensor and use the same processor.
They have the same ISO range, as well as the same shutter speeds and flash sync speed.
The D500 is better built and has higher durability rating (200,000 shutter actuations vs 150,000 clicks with the D7500).
D500 has a bigger image buffer... up to 200 RAW files, compared to 47 RAW with D7500.
D500 has a more advanced AF system: 153 points (99 higher performance "cross type". D7500 has a 51-point system (15 cross type).
D500's AF system is rated to be able to focus as low as -4EV light levels. D7500 is pretty good, too, but a little less with -3EV rating.
Both have 100% viewfinder, but D500's has slightly higher magnification. 1.0X versus 0.94X in D7500.
Both have articulate, 3.2" (diagonal) Touchscreen LCDs... but the D500's is much higher resolution: 2.3 million dots versus 922,000 in D7500 (which was a decrease from D7200, too).
D500 is "f/8 capable" with 15 of it's AF points. The D7500 has only one f/8 capable point at the center. This has to do with using teleconverters on lenses. A 2X on an f/4 lens or a 1.4X on an f/5.6 are both "f/8 combos". (Note: Some DSLRs are less capable than either D500 or D7500... Some are limited to f/5.6 combos, limiting use of teleconverters.)
D500 also has dual memory card slots, where the D7500 only has one. (D7200 had two, too.)
And, D500 has faster frame rate (up to 10 fps versus 8 fps with D7500).
D500 gets approx. 30% more shots per battery charge (see note below, regarding D7500's built-in flash).
Plus there is an MB-D17 vertical/battery grip available for the D500, which can double it's battery capacity for longer shooting, improve the ergonomics for portrait oriented shooting and can even feel better balanced when shooting with larger telephotos lenses. Nikon doesn't offer a battery grip for the D7500... There are some third party grips (such as Vello BG-N18), but they are sort of "MacGuyvered", because the camera really isn't set up to work with them. This is rather weird, because Nikon offered the MB-D15 battery grip for the D7200, the model that preceded the D7500 (according to Nikon... some reviewers and users considered the D7500 a downgrade from the D7200 in some ways... not really a replacement).
Among the few advantages of D7500...
.... D7500 has a built-in flash. Those are wimpy, low powered, slow recycling and in the worst possible place for redeye and ugly shadows. They also rapidly drain the camera's battery. D500 doesn't have a built-in flash (which probably is why the D500 is rated to get a lot more shots per battery charge). An accessory flash solves most of the problems, especially if it's used on a flash bracket that positions it a little higher up and slightly off to the side.
... D7500 is rated to do slightly higher ISO by DXO Mark. Since they use the same sensor and processor, this is probably due to different firmware and image processing algorithms in the 15 month newer D7500. It's not a big difference, but possible that something as simple as a firmware update to the D500 might make it equal or better. (Note: The now discontinued 24MP D7200 not only has higher resolution than either, it also has greater color depth and higher usable ISO.)
... D7500 weighs less and costs less.
Tell your friend it's a bad trade. Swapping a D500 for a D7500 is a downgrade... not an upgrade!
EDIT: Damn, just saw your followup clarifying that your friend is looking to upgrade from D5100 to D7500... that's a completely different story! D7500 would be a solid upgrade in many ways (but, depending upon what your friend shots, a D7200, which can be hard to find since they've been discontinued, might be an even better upgrade!
Rather than go through the differences item-by-item, see how the 6 year older D5100 compares with the D7500 here:
https://cameradecision.com/compare/Nikon-D5100-vs-Nikon-D7500