I am planning to get the 15 inches model, but I am unsure if I shall go all the way up for the 512 MB model, or if it is enough to stay with the 256 MB model.
Somehow I think that the 512 MB model is a safer bet in what concerns the laptop longevity, however since I only do graphics programming as an hobby, I don’t know if it is really worth it.
It didn’t stop me before, now of cause it does help to have 512 as you can have more enourmous textures but it’s not a must and there are ways around that.
On the flip side a lot of things we used to rely on VRAM for can closely be emulated by some of the nice Apple ‘fence’ instructions which effectively map more memory to the GPU, and also caching hints. It’s not more VRAM, but it’s not far off in real world use… And working within constraints will make you find new and better ways to do things, which builds experience. Although taking that argument to it’s logical extreme you should go buy an iPhone and develop on that.
I’d take a look carefully at the actual GPU / MBP specs though.
Not sure which machine you are considering but if it’s a laptop the last time I checked the lower end MBP 15" does not have the “dual GPU” option.
Multisampled MRT for deferred shading can push VRAM budget, but anyway the gpu can access SysRAM textures quite nicely. In a test, I loaded and displayed 1.5GB texture-data in a scene on a 256MB gpu, with just a tiny slowdown - once there’s been a z-pass.