I would say that your memory usage is the biggest issue here, as I have the same problems on my own computer (4GB RAM) and I face some pretty nasty graphics lag when going through animations like boss appearances/fights, the slot-machine spin, and a few "movies". It was much worse on my 2GB RAM laptop which I don't have anymore (for that one, Aigis was outright unplayable, this one it runs battles at half-speed).

It's strange though, Chrome shouldn't take up THAT much memory unless you have it doing something heavy-load other than the flash program. Try having the game as the only tab and if the resource usage is still extremely high, it could be a Chrome-related application that isn't blatantly visible to users, to which you should consider disabling chrome extensions that work on the side (like hangouts, antivirus scanner attachments, etc).

Ultimately, if you just want the problem gone and gone, you could probably fix it by boosting your RAM to something redundantly high, like 12GB or 16GB. I have a 2-year old Desktop running Win 8.1 with 16GB and graphics lag was never an issue so I doubt it's CPU/GPU related.

Course, like everything I say, take it with a grain of salt. My knowledge of this field is fairly outdated, if I say so myself and someone else may have better advice to bring to the table.