MBA 13" running Lightroom

I've been in need of a new laptop for some time now, and would like to maybe buy the new MacBook Air 13" for travel. I already have an iMac and a 2008 model MacBook pro (which my will be given to my cousin for school),. With this new MBA, I'd be running Lightroom 3 to do some RAW to jpeg processing on the road. I'm not sure if MBA will do the job? If anyone has experience with MBA, I'd like to hear your thoughts. Budget is a constraint, but if it's worth it, then I'll have to come up with the cash. Here are some other concerns:

• i5 or i7?

• definitely 8MB RAM

• is it worth it to spend another $500 to upgrade SSD to 512GB?

Thanks in advance for inputs.