I tend to think saying your PSU is overkill is like saying 8GB of RAM is sufficient, but even more short-sighted since PSUs better transfer to new builds than basically any other part. Stick with the 1000W PSU.
I definitely agree that PSU's are the most "future-proof" of all components. The reasons are two: first, because they're on the ATX standard, which isn't going anywhere, and most ATX PSU's will fit in just about any eATX, ATX, and MicroATX cases, and even some MiniITX cases! Second, because they aren't tied to the aspects of circuitry which have a higher turnover of relevance like CPU socket, DDR slot, PCI standards, SATA, etc. The same major power inputs have been steadfast for over a decade (with minor expansion that could be achieved with the previous setups if adapted), and aren't changing anytime soon that I can see.
Having said that...if you know that you're never going to be one of those guys that runs a triple-GPU configuration, or a heavy overclock with dual-GPU, then why would you waste money on a 1000w PSU? You're
never going to use it. If you ever decide that you will, then the $200-$250 or so for that kind of PSU is really something of a trivial cost in an upgrade of that ambition where you'll likely be spending ~$1000 on GPUs alone. In that situation, you could either sell your old PSU, or more likely I bet you'd find yourself using it to power the PC you're replacing that you'll move elsewhere in the house (or to sell), or perhaps to save cost on an HTPC you'd slap together as part of your major overhaul.
*Edit*: allow me to demonstrate my logic
Otherwise, in the meantime, the Corsair CX600 is just $70, and is more than enough to power any single-GPU setup in existence (even with an overclock of the CPU). That H1000 is $220. This $150 difference in his current setup could upgrade him from a GTX 970 to a GTX 980, or even buy him a second SSD (perhaps even a PCIe SSD, the fastest in existence, to host the OS so that his Samsung could be dedicated solely to applications and games).
*Edit #2*
And now, paying attention, herpaderpmick, I see that he already ordered the PSU. LOL, I'm such a tard. Well, you're set for any upgrade you could conceive, Krauser, and your energy efficiency will be off the charts.