7yr Old iMac to $1200 iMac 21.5" Good Enough?

I have an older iMac and Macbook Pro, both about 7 years old. The iMac is acting up and I'm left doing most of my photo work on the 17" 2.16 GHz MBPro.

I'm looking at the subject $1200 entry level iMac for all my photo needs. The new machine would be running the new LR4 to edit/manage Nikon V1 RAW files, backing them up to an external drive. I don't plan on using Photoshop or other 3rd party software, but I would like to be able to do something with Nikon .MOV movie files, too. Only other thing I do is routine web browsing.

I suspect I'd see a big LR performance increase compare to what I'm using now?

For what I do is:

• 2.7GHz worth the extra $300 when compared to 2.5GHz?

• standard 4GB RAM good enough?

Also, does the machine come loaded with any means to calibrate for a decent monitor color profile? If not, what are people using these days to create a monitor profile? I'd say I don't need absolute precision for a color profile, so something that's EASY would be appreciated.

Finally, considering where I'm coming from with the 7 year-old technology, is there anything I need to look out for in a new machine that might surprise me in a bad way?

Thanks.