Well, I finally got to try the game (stayed up until 3 AM my time just to be able to start downloading; stupid uplay). Right now I'm only using one GTX 970 with my i7-3770K at 2560x1440. I'm monitoring FPS, GPU/CPU core usage, and VRAM usage with MSI Afterburner as well; the game hits my GPU hard at this resolution. Turning every setting down to low at this resolution nets me about 50ish FPS after a brief glance running around the starting village; high textures, shadows, and environment details with HBAO+ with FXAA are getting me, just running around, about 35-45 FPS with some dips to around 30 in some in-engine cutscenes.
I am fairly disappointed in the lack of setting options. There are some, but not very many. Now, the game is playable like this and I honestly think it's arguably the most visually pleasing game I've seen (partially due to the setting). There are so many NPCs and they nailed the general look and feel of French architecture. At my resolution, blur is minimal and it's just an overall very aesthetically pleasing game, if a bit inconsistent in some areas (NPC pop-in, blurry distant textures). I'm not getting 60 FPS like I could in Black Flag with a single 970 and a few alarming dips (cutscene) to about 26 FPS have me worried that even SLI 970s won't hit 60 minimum. I can only hope SLI scales well with the game. High textures cause about 3100 MBs of VRAM usage, Ultra High about 3700-3800 and actually lower performance from what I briefly saw. Gsync owners are in for a treat, unfortunately I'm not one (PLS panel).
I can confirm that the game is GPU-bound for me, surprisingly not seeing my 3770K limit things (it's at stock right now for testing purposes). If I lower my resolution to 1920x1080 and keep the same generally high settings with FXAA I listed above, it sticks to 60 FPS just running around with my G1 970's usage hovering about 65-85%. I expect it to dip a bit below in cutscenes. Obviously I'm not playing at that resolution though, so I look forward to the second 970. I should be able to mess around with it tonight, but it'll be about 8-9 hours from now.
If anyone is curious about anything in particular (setting/res combo, single vs SLI 970 performance, CPU usage, VRAM usage, etc.), I'd be happy to check and report back.