Will having a 12-inch laptop screen hurt my productivity?

I currently own a Sony Vaio VGN-FS920, 2G RAM, Intel Centrino. It's still a great computer, and my very first, but it's beginning to get a little sluggish when I multitask. I'm a webdesigner, college student, and extreme multi-tasker. It's a 17" screen which is awesome, but a little big to carry everywhere. I'd love a 14-15".

My school has given me a $1200 grant for a new laptop. Things that are important to my decision: 3-4G RAM, Good processor, s-video out, weight.

I've gone shopping online and have narrowed my decision down to a few (though I'm open to other considerations).

HP Pavilion dv5-1000us 15.4"
(a good balance between power and portability)
http://www.circuitcity.com/ssm/HP-Pavilion-dv5-1000us-15-4-Widescreen-Entertainment-Laptop-FE850UA-ABA/sem/rpsm/oid/215030/catOid/-12963/rpem/ccd/productDetail.do

Acer AS6920-6508 16"
(seems seems powerful and able to handle what I do, but a little weighty)
http://www.circuitcity.com/ssm/Acer-AS6920-6508-16-Widescreen-Laptop-AS69206508/sem/rpsm/oid/215816/catOid/-12963/rpem/ccd/productDetail.do

Sony VAIO VGN-CR510E/R 14.1"
(I love the way this computer looks, the red and the keyboard)
http://www.circuitcity.com/ssm/Sony-VAIO-VGN-CR510E-R-14-1-Widescreen-Laptop-Red-VGNCR510ER/sem/rpsm/oid/215089/catOid/-12963/rpem/ccd/productDetail.do

Now here's the computer I've actually fallen for and the main reason for my question, normally I'd be able to decide but this has got me stumped.

HP Pavilion tx2510us 12.1"
http://www.circuitcity.com/ssm/HP-Pavilion-tx2510us-12-1-Touch-screen-Entertainment-Laptop-FE912UA-ABA/sem/rpsm/oid/214774/catOid/-12963/rpem/ccd/productDetail.do

I've read reviews and researched the AMD processor. It seems like it would be able to keep up with me, especially if I upgrade the RAM.

I'm not to concerned with it getting to hot, and I've actually gone and seen this in person. The keyboard doesn't seem to small. Compared to other laptops, it seems just as powerful. It has a better graphics card than most. I stare at a screen all day, my life is in my computer. Will having a 12-inch laptop screen hurt my productivity? Is the tablet functions of this laptop worth giving up the extra screen size?