Depends on the games in particular. The 5450 was a low-end card (similar to the old 6450/7450 I used to have). Don't expect to be able to play BF4 or other similar games, & I'm not even sure how well it would run BF3 or similar games even on low settings. Of course, the RAM & CPU also have a huge effect on that.
But remember, you are very close to the minimum requirements so might get a lot of lag sometimes. Anything more intensive than that would cause a lot of problems.
And as for the GPU, there's really no point in getting anything stronger since the rest of your system won't be able to handle it.