Dual monitor Vram impact

Hi all

Since the new Macbook Pros are out I'm about to purchase one. I would go with the lowest model because i think that the 500€ difference aint worth it for me.
Only thing making me hesitating is the +128MB VRAM. I plan to use the macbook pro in dual display mode with my 21" TFT and plan to go 30" in the future.
I read through many 128 vs 256 threads here on the forums and most comments related to the 3d performance. I have to say im no gamer so 3d performance would be a criteria for me. As far as i read the vram is divided evenly across the displays, right? So my question is, will even be 64Mb (128MB vram model) be enough for a smooth mac OS X desktop with all its eye candy?
Or is this eye candy already on heavy 3d use, thus needing more VRAM?

thanks in advance.

I found an excellent article http://arstechnica.com/reviews/os/macosx-10-4.ars/14 . It emphasizes the role of VRAM for Tiger. But then again they don't mention how many Megabytes are typically involved. I know i could just do the math like - 1600x1200x32bit = 7.680.000 bytes = 7,5 MB for one frame buffer on my 21". I might think that even 64MB per screen looks like plenty of VRAM, but i dont know how many "layers" of frame buffers are used for all the eye candy in Tiger (probably even more in Leopard).
I would hate to have 128MB and purchasing a 30" in 2 years just to find out that everything runs sluggish with that amount of vram. On the other side 500$ premium just for additional 128MB (i know +40gb hdd, +0.2 GHz CPU, but these are not important ot me) is hard on my budget.