PPI is a function of the resolution over diagonal size. a 27" 2560x1440 display will be around 109ppi and they typical 2560x1600 displays are also 109ppi.
For desktop restate, the 2560x1600 will give you an additional 160 vertical pixels, however in games its dependent on how the Field of View is calculated. One example would be Borderlands 1 would crop its view space to keep its FOV the same between 4:3 and 16:9. But in Borderlands 2, its FOV is calculated against the height and as such going from 4:3 to 16:9 would yield a larger field of view. These effects will occur when comparing a 16:10 display to 16:9, however the magnitude of their impact will be greatly diminished from how minor the aspect ratio differences are.
PPI...