Windows 10 Mobile is not "actively being supported" by Microsoft, which means these updates are not really tested let alone optimised for older phones. Only the phones such as the 950, 950 XL, Elite X3 will see some what more focus in terms of "optimisation".
If you wish to stick with WM10 then these are your only best bet at present, despite the fact the hardware of older Lumias such as the Lumia 930 and Lumia 1520 still work flawlessly.
I have two Lumia 930s and both work (but definitely no longer daily driver useable), albeit both are not going to get anything beyond the anniversary update however it does get security updates. Wether or not they are optimised for the L930 is another story entirely.