General: Celeron-bad Choice?

I'd like to buy a Subnotebook (12.1" size) and found one for somewhat <400€ from the same dealer where my brother bought his 13.3" Laptop. I have the choice between the Celeron M 585 and a Pentium Dualcore T 4200 as CPU, the Pentium version costs additional 30€.

As far as I know, the Celeron (31 Watts TDP) doesn't provide power saving options, so the power consumption might even be higher than the one of the Pentium (35 Watts TDP). I won't need the dual core and it is more than odd, but should I buy the more powerful CPU just to be able to reduce its clock speed that the battery lasts longer?

My lack of money finally made the descision for me, I had to give the Celeron a try.

The Notebook arrived last week, but I'm not at home and was not able to test it yet. So, I asked my brother to run some tests for me. The battery doesn't last as long as promised (but I expected that and somewhat about 3h in office is okay for me). The system performance seems to be not overwhealming (of course), but fair.
Maybe I have to add that I am used to working with my old Win 98 Celeron 550 MHz Laptop.

My brother also reported, that it's quite light weight (~1,8kg), silent and it's not getting as hot as his Notebook. Also, the battery of my Notebook lasts slightly longer (OK, his Notebook is more powerful with a better video card).

I'm looking forward to find out during the next weekend how much performance a Celeron 585 and a X 3100 Intel Media Handbrake uhm... Accelerator Graphics has to offer. As far as I know right now, it matches with my expectations for a 390€- Subnotebook. If I would be disappointed, I could still give it back and take my cash again.