Moving to a R9 270X will be a night and day upgrade, for games.
Just bear in mind the R9 270X needs a strong power supply, most need dual 6 pin PCI-E leads to run.
If the PSU isn't that strong, a R9 270 is slower but most only need the one 6 pin lead.
If the PSU has no PCI-E leads or is some cheap, nasty thing, swapping it would certainly be a good idea.