Hard to say. I have the Sapphire 580 Nitro+ (which I think is quite similar to the Pulse) and I really like it. At 1080p/high settings (which the 570 is best suited for) 4GB is usually enough, and if it's not I think you should be able to work around it without too much difficulty by tweaking a few settings (like texture levels). If you're ok with that 4GB is probably fine.
On the other hand if you have good case airflow and/or low ambient temperatures, the cooler on the Armor may be all you need. Or if your PC has good sound insulation, it's not too close to you when you're gaming, and/or you game with a headset then the noise may not be an issue if the fans have to ramp up to keep it cool. I don't know if it's really cut out for overclocking though if you're interested in that, would probably get hot and noisy pretty fast. As I mentioned, I'd sooner undervolt that card than overclock.
Edit: If you don't necessarily need to purchase right away, this can be a good place to watch for deals on graphics cards (and other components): https://www.reddit.com/r/bapcsalescanada/