Leap from PC to MBP, advice

I am in need of an upgrade... currently editing photo's on an 8 year old Dell PC... can you say frustratingly slow? I'm looking to buy a new computer that will be dedicated to my photo work, post processing for clients and one the family won't touch. I was planning on a laptop to use with external hard drives for storage and while I currently use LR, was thinking if I got a MBP, i'd switch over to aperture.

Any advice, comments... My thoughts are (being on a limited budget) MBP 13" with the 2.9 i7 and 8gb RAM. How does Aperture compare to LR?

While I would love to have the new "retina" screen and all the new goodies... I can't afford getting up to 3-4K on a unit.... If I go with a 13" MBP as above am I making a bad purchase?

Appreciate comments and suggestions.

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Lee Wiren