Just thought I'd stop by and let you know that I decided to go with the 1000w PSU. I remembered that the old adage "more is always better than not enough."
While more certainly doesn't hurt, I think the days of 1000W PSU (even 850W) are numbered. CPUs are not as power hungry, and neither are GPUs. On top of that, multi-GPU setups are less and less supported, and that greatly reduces the need for large PSUs.
IMHO, a 650W PSU is probably more than what most people will need going forward.
Have fun with your new build. When you're done, be sure to post some pics - I love seeing what other people are building. And if you run into some roadblocks you overcome, be sure to discuss those, too. Hopefully, it will help someone else later on.