Best imac for Logic Pro 9

Hey!

What do you think it's better option for recording with Logic Pro 9:

(I also use MainStage, Ableton Live, Sibelius 7)

iMac 21.5" QC i5 2.7GHz/8GB/1TB/NVIDIA GeForce GT + buying 8 GB more RAM= 16 GB RAM

or

iMac 21.5" QC i5 2.9GHz/8GB/1TB/NVIDIA GeForce GT

d_N