you won't be playing TW3 with a 750ti at any resolution... probably not shadow of mordor either.
TW3 requires atleast a GTX 960; and shadow of mordor requires a min of 3gb of vram; which really limits your choice of gpus.
a gtx970 will play both in 1080p. a 960 will manage (60fps) in 900p. on the amd side the r9-280x will probably manage both fairly well with some tinkering at 1080p, it won't be maxed but it will be something playable.