I was in the same boat a couple of months ago and i went with the 13/4/128
This was my reasoning:
Both were nearly the same price - but if i went with 11" the advantage i got was the small size / ultraportability - but the odd screen size wasnt very helpful in working on any office docs (too much scrolling needed)
With the 13 mentioned being nearly the same price (a bit cheaper through macmall) i not only got a faster processor vs 11 but also more screen area, faster fsb, SD slot and larger trackpad. And its not that 13 isnt portable. I went with the 13.
Now when i look back, had i gone with 11, i would probably have had buyers remorse.
You have to check your own priorities ofcourse.