The big difference between the 2-core D-1508 and the D -1537 is cores and clock speed. There is a 10W TDP difference as well but unless you use all the cores all the time, I doubt the heat nor the power will be all that different.
I found my D-1537 board to be VERY finicky re memory. As in find the EXACT spec down to the last digit in the SKU from the approved hardware list or the system would only recognize two out of four DIMMs.
I did not have any luck running the ZoneMinder or whatever CCTV package in a jail. Running blueiris in a windows VM was unsuccessful as well. It could very likely be my inexperience that was the issue. But I got the sense that the 1.7GHz cores made it too easy to miss an event due to being overtaxed.
Heat wise, I replaced the CPU HX with a Cu version and an active cooler. I also added a bunch of fans and some tape to direct air flow, etc. See here. This was not necessary, it was just a design goal to have the system run relatively quietly but cool to maximize lifespan. Without scripts, the CPU rarely cracked 40* C, the HDDs hardly ever got above 30* C.
No issues with heat, and I subsequently adopted @stux script which makes the fans a lot quieter. FAN1-4 on the motherboard is dedicated to the CPU and rear case fans, FANA runs the three fans cooling the HDDs, FANB powers the little fan I strapped to the HBA.
The primary reason I advocate the -2C- version of this board for file server use is price and clock speed (which helps SMB) in my pokey 1VDEV system with a little sVDEV it gets up to 400MB/s sustained write speeds. So the slower clock of the D1537 doesn’t seem to be the limiting factor re: transfers.
Maybe I will find more uses for the cores when I have to move to SCALE. in the meantime, they lie fallow.