CPU: Intel Core i5-2500k @ 3.8GHz (4.5GHz on offset started to BSOD every few days)
GPU: EVGA GeForce GTX 760 (ACX Cooler edition)
RAM: 12GB G.Skill Ripjaws DDR3 @ 1333MHz (2x 4GB + 2x 2GB)
Storage A: Samsung 840 EVO 256GB (Windows + Programs)
Storage B: WD Caviar Black 1TB 7200RPM (Media + Games)
Motherboard: ASUS P8P67 PRO Rev B3
PSU: Antec Earthwatts EA-650 650W 80+ Bronze
Display: ASUS ML239H 23" 1080p IPS
And for shits and giggles, my periphs:
Keyboard: Rosewill RK-9000 CherryMX Blue
Mouse: Logitech G502 Proteus Core
Webcam: Logitech C270
Speakers: Logitech Z313
Headphones: Superlux HD681 EVO
Microphone: Blue Snowball
Other:
-Wacom Intuos 4 Small
-3DConnexion SpaceNavigator
I run at full ultra (in a maximized window) with 2x the default ultra shadow resolution. 256 draw distance, and 6 non-impostor avatars (Believe it or not this setting actually makes the most difference, because avatars are basically FPS black holes). I keep DoF off unless taking pictures. Depending on the number of avatars I get anywhere from 60 FPS when alone in a well built sim down to like 12 in a crowded area. Avatars are -that- bad.
As for your GPU debate I've heard from a couple of GTX 970 owners that SL runs like total garbage on them. One friend said his HD6870 was faster when it comes to SL. My guess is for some reason SL is writing to the gimped memory buffer all the time instead of using the fast memory first, it's the only thing that makes sense with that specific card, so between those two, I'd suspect AMD's Nodrivers is the lesser problem. Personally I'd save the extra $100 or so and go 980, it's bound to run better than both of them.
It's also worth noting that SL is very CPU bound, so make sure you're getting a strong CPU (I'd go AMD 8350 or better or Intel Core i5 or better). If Intel go for a strong unlocked model, overclocking actually makes a bit of difference in SL.