The 7750 is more than enough for your 1440x900 monitor. The resolution you set on your windows is already the resolution playing at your monitor. It is fine because that is the native resolution of your HP w17e.
Just take note that there are 2 types of 7750:
1. 7750 @ 800Mhz
2. 7750 @ 900Mhz with 1x6PIN PCIe.
They are supposed to be priced the same so if your power supply have 6PIN PCie connector, go for the 900MHz version. Otherwise, get the 800Mhz.
Does the 1x6PIN PCIe version draw more power than the regular one?
Also is PowerColor a good brand?