The hardware is a now thing, certainly not 5 years. I don't mean to be disparaging of your system which is quite low end.
Normally I don't advertise my system as I think system sigs are a bit sad but for example my i7 4790k 4-4.4 Ghz, twin GTX 970's with 16 Gb ram, OCZ ssd based system, which while capable, is far from a current "top end" system and gets 100-120 fps inside stations, 140-150 in SC with all graphics settings maxed @ 1920 x 1080 and SS (super sampling) set to 2. When I run 3 monitors @ 5890 x 1080 and I drop SS back to 1, leave all other settings maxed and achieve similar to slightly better framerates. With SS at 1.5 slightly lower framerates. but on all settings the gameplay is as smooth as glass.
There are i7's and there are i7's though mate also your graphics chip is getting a bit long in the tooth as well. Toss a 970 or a 980 in it and you will really notice the difference.
Well, if you are getting framerates of 30 or above it should be smooth. 30 frames per second is what TV shows and movies have been filmed at for years and they are smooth. You start getting jerkiness at below 30 fps. So long as I can consistently get 30fps or above, I'm happy. Sure 60 or even 90 fps is good, but it's the same as listening to an MP3 song encoded at 256 kbit/sec as opposed to 320 kbit/sec. Unless you have ears with the sensitivity of a dog, you won't hear any different, but the 256kbit/sec takes almost takes substantially more space.
And yeah, I know my machine is quite low end. I'm going to be getting a better one that will be almost recommended specs. Not quite, they recommend an AMD R9280X. The machine I'm looking at is an R9 280, but with a hex core processor.