QoS will be really helpful given your speeds. If set-up correctly, it'll improve everyone's browsing experience and keep pings low for all. As it is, even a video or an app update on a phone can saturate your connection (and cause high pings / laggy browsing).
I'm going to show you my setup that has worked really well for us, and you can do it in like 2 minutes. It keeps everyone's downloads equal and pings low for all, regardless of device or port (just in case your games use some random ports and you don't want to mess with those).
Go to QoS Upload under Firewall and turn it on. Delete all rules. Set default service class to Normal. Delete all service classes except normal. Set Normal to 100%. Set your upload speed. This is very important because Gargoyle can't determine it for you. It needs to be a little lower than what you get for upload speed tests. Maybe 600kbps?
End result should look something like this, except with your upload speed.
Save your settings and move on to download QoS. Delete all rules and set default service class to Normal. Delete all service classes except Normal. Set Normal to 100%. I do not recommend Min RTT for your connection because your speed is already slow; it would make it even slower (plus the difference isn't much at all; 10ms for me). Set your download speed. This one you can set at the max you've ever seen or even a little higher. Maybe 2000? You're the one that knows how fast your speed can go. By using ACC, Gargoyle will find out the correct download limit (unlike upload). End result should look something like this, except with your speed:
Scroll lower to ACC. Activate it (first checkbox). You can leave the rest unchecked. Later on if you notice your ISPs server doesn't work well to determine your download speed, you can change it to Google DNS or OpenDNS (8.8.8.8 or 208.67.222.222). Not sure what's more stable down under. Save your settings.
All done. Go start a big download somewhere (perhaps an Ubuntu ISO? Anything that'll max your connection for a few minutes). Go back to your QOS Download settings page and take a look at ACC section at bottom. If correct, it should be determining your speed correctly (something around 1200 to 1400 in link limit). Refresh page if needed. If it's not working well, see above and switch ping target (second checkbox) to Google DNS or OpenDNS IP. Once you see it stabilize, start a speed test on a different device and you should see that your pings stay slow and download speeds split evenly between devices. This is nice because you don't have to worry about what ports your games use, or what device IPs to limit, etc.
That'll get your started (frankly, it's the QoS set-up I've used for years and ever since then everyone in my family has been happy). If you want to limit other devices and what not, I'll let someone else guide you thru that, but be careful or otherwise you'll leave all the other devices with nothing.
Whenever I'm on a slow / high ping cellular or WiFi network I always think to myself "If only they used Gargoyle..." 
