Is 7010's PCIe x16 slot only Gen 2.0? Can I upgrade to 3.0?

I have two Optiplex 7010 Mini-Tower PCs (one with an Intel i5 and one with an Intel i3).  The original technical specs for this model say that the PCIe x16 slot should be PCIe Gen 3, but HWINFO64 and CPU-Z x64 say they are Gen 2. 

In one of these PCs (with the Intel i3), a Samsung 970 Evo Plus 2TB NVME M.2 SSD that I have connected to this slot via an adapter card is doing a read-write test at approx. 1,700 GBps instead of an expected 3,500 GBps.  (See this very good article:  "Install and boot from an NVMe SSD on a Dell OptiPlex 3010, 7010 or 9010" .)

1. So, why do my 7010s have only PCIe Gen 2 in the x16 slot, and is there anything I can do about it?  Is there any way to upgrade this slot to Gen 3.0?
    
2. Now let's look at the x4 slot.  HWINFO64 and CPU-Z x64 don't even report what Gen it is, so might it even be worse than Gen 2?  I also tried the Samsung 970 Evo Plus 2TB NVME M.2 SSD in this slot, and it ran a little slower than in the x16 slot, at about 1,450 GBps.
    
3. As I like to save money for a family business by buying used Optiplexes and modding them to be better, which are the first Optiplex models that definitely have Gen 3 in
   (a) the x16 PCIe slot and
   (b) the x4 PCIe slot? 
   (And I mean the first sub-model in each of the 3000, 5000, 7000 and 9000 families of Optiplexes.)

Thanks.