I'd recommend skipping the R7 240 as it's a terrible value and near worthless for gaming, plus it requires a PSU upgrade. I realize this is the AMD subforum, but your best choice would be to pick up a 750 Ti, one that doesn't require an external power connection. Way faster than the R7 240 and probably cheaper/easier since you won't need a new PSU (assuming you haven't already bought the PSU).