I was wondering whether the MSI Radeon R9 280 3GB TWIN FROZR would be a good match with the i3-4150 3.5GHz Dual Core processor or whether I should downgrade the GPU a little (maybe perhaps to a GeForce GTX 750 Ti)?
That should work just fine, just make sure you have a power supply that can support the r9 280 a good quality (XFX, Seasonic,EVGA B2 or G2, or superflower) 550w PSU would be ideal.