Get the 15". For your purposes the 13" flat out sucks in so many ways. Games feeling unimpressive due to display size is the least of those. If you are either a programmer for game engines such as Unity or 3D modeler/animator that uses rendering, then get the 15".
Also note that setting adequate effective resolution for Unity on the 13" rMBP will murder the GPU. The "standard" setting on the 13" rMBP is equal to 1280x800, but you need 1440x900 (Air's native res) at the very least, preferably 1680x1050. How Apple's retina resolution scaling works for nonstandard resolutions is that it renders at twice the resolution you set and downscales. So then you are actually doing realtime 3D rendering at 3360x2100. I don't see how the 13" rMBP's integrated GPU could possibly handle that without choking.
The dedicated Nvidia GPU on the 15" is far superior to the Intel integrated on the 13" rMBP, more so than simple "average FPS" benchmarks would tell you. Quadcore CPU vs dualcore CPU isn't a small issue either.
I hate the fact that the high end 15" is the only laptop in current lineup with a decent GPU. Why no 13" model with a decent GPU? Why no cheaper 15" model that has a decent GPU and a 1680x1050 non-retina display? (I think this could actually be better in practice than retina specifically for working in Unity or doing heavy 3D modeling.) Even without a performance difference, I'd pay extra to have a Nvidia GPU on my light/small laptop because Intel's OpenGL support remains **** in comparison.
Also note that setting adequate effective resolution for Unity on the 13" rMBP will murder the GPU. The "standard" setting on the 13" rMBP is equal to 1280x800, but you need 1440x900 (Air's native res) at the very least, preferably 1680x1050. How Apple's retina resolution scaling works for nonstandard resolutions is that it renders at twice the resolution you set and downscales. So then you are actually doing realtime 3D rendering at 3360x2100. I don't see how the 13" rMBP's integrated GPU could possibly handle that without choking.
The dedicated Nvidia GPU on the 15" is far superior to the Intel integrated on the 13" rMBP, more so than simple "average FPS" benchmarks would tell you. Quadcore CPU vs dualcore CPU isn't a small issue either.
I hate the fact that the high end 15" is the only laptop in current lineup with a decent GPU. Why no 13" model with a decent GPU? Why no cheaper 15" model that has a decent GPU and a 1680x1050 non-retina display? (I think this could actually be better in practice than retina specifically for working in Unity or doing heavy 3D modeling.) Even without a performance difference, I'd pay extra to have a Nvidia GPU on my light/small laptop because Intel's OpenGL support remains **** in comparison.