Homelab

The 730 will be more efficient based on improvements to the chip design but also DDR4 uses less power than DDR3. There's also increase in efficiency when with the v4s over the 3s

The newer chips improve efficiency in two areas. a) what they do per clock cycle (IPC) and b) power consumption at low load or idle.

Chips like the v3/v4 in the 13th gen do lag on IPC but also on pure clock speed but for most homelab servers that doesn't matter because they're not heavily loaded. It's the power consumption for idle where they get crucified and yes the Xeon will use a lower more power to tick over.

There could also be a design factor there. It's okay if your desktop goes into a deep sleep to save power but for a server responsiveness is a big factor and you don't know when there's going to be access so going in really low power mode isn't a good thing because the time to come back to full power could be critical.

if you search for online power consumption caculator such as one used for sizing a a UPS you can play with different configurations and see what numbers you come up with.

And yes easily $70 more to run the 710.

But there can also be other factors. Each of the those HDDs can consume between 5 and 10w depending if they're idle or in use. Each memory module will use 2 - 3w so if you've 8 x 8GB in the Dell server that's 24w, where as say 4 x 16GB would use half that.

Your Dell also has iDrac so even if the server is shutdown, unless it's unplugged you'll still draw some power.

And speaking of power, the PSU effeciency has greatly improved over time. Not sure what standard PSUs Dell provided with the 710 and whether they improved them to 730 but there's a good chance your desktop has a more efficient unit.