Best PowerEdge Upgrade Path On Home Network

I'm asking this question on behalf of a friend of mine; both of us are tech enthusiasts with a flare for the Dell PowerEdge scene. We have had dell PowerEdges of various types for ages now, but now my friend's realizing the power consumption impact that running two R610's has potentially wrought on the environment, and wants to step his infrastructure down a notch or two. I suggested a T330/340 (this is not truly a business network, so having the latest, greatest, newest, isn't as important as it might be in some other scenarios), and I'm wondering. How do those stack up against the older X10 series in terms of power consumption and enviornmental impact? I know that all of the X20 series or above are fresh air compliant, but what does actually mean in practice? 

Initially my friend wanted to go with two OptiPlex desktops to be used as servers instead of actual server models, though I think eventually the limits of those are going to get hit, considering how much stuff we're always playing around with. So, trying to gather everybody's thoughts. I have an old T110, myself, which I outfitted with a T110 II board several years ago, so with his expanded ram count, now, I could probably keep him going a bit longer, but I'm going to eventually hit the upgrade need to. Our main network consists of a domain controller at each site (or two), one at mine, one at his, and we used to have one in a datacenter near us, but we recently shut that one down because datacenter infrastructure isn't cheap.  We have a pile of docker containers kinda all over the place with various things hosted on them. So my thoughts are to work up to T300 series servers instead of desktops. What does the community say?