As a classic example of YMMV, I've used a 17" MacBook Pro and before that a 17" PowerBook for several years, for the screen real estate. It's my only computer, which makes it also my only travel computer. I use it in coach seats as often as not. Takes a bit of wiggling, it helps that I'm skinny, but it works. Saving four pounds of weight would be nice, but for me it's way back of screen size in importance. (The fact that I'm one of those weirdos who walk up great big hills with a great big pack may help, but I think I'd want it anyhow.)

I do basically the same things the OP does, except that the coding is mostly JavaScript (unrelated to Java, despite Netscape's attempt to capitalize on Java's popularity by picking a related name) and VB. Having room for multiple windows is, for me, a biggie.

I say this not to claim that I'm right and others are therefore wrong, but to emphasize that this is totally a matter of taste. There is no substitute for seeing if it fits your working style. Since you can try both, I'd go for it. If for any reason this isn't practical, I'd start with the 11" and move up if it's not big enough.

Macs tend to hold their value better than Windows machines. I'm part of the reason: almost always buy used, in part so I can afford a 17-incher and have some money left for travel!