The NAS generates heat, so it will always run hotter than the ambient temperature. Using drives that are more power-efficient does reduce the system and drive temps.
SSD power use varies considerably by model, often ranging between 1 watt and 4.5 watts under load. This overlaps the HDD power use - NAS purposed and enterprise class drives generally run between 4 and 6 watts.
The operating temperature range of the disks also might be a consideration. Many SSDs are spec'd to run at 70C, hard drives are usually spec'd at 60C.
So you'd need to check the specific specs of the drives you are considering, and perhaps take both power and the operating temperature range of the disks into account.
How that relates to the data sheet is a bit hard to say, since there always is some margin built into those specifications. But whatever disks you choose, it's best to stay under the current datasheet's ceiling (45C).
How hot are your ambient temperatures? 45C is pretty hot.
Definitely over the spec, and I'd be concerned about the disk failure rate of HDDs in that temperature range. Even though the disks are spec'd to run at 60C, there is some evidence that the failure rate increases significantly if they are running at 50C or above.
I suspect Netgear wouldn't guarantee operation at that temp, and likely would void the hardware warranty for a NAS running outside the operating temperature range.
