I currently have 4GB of RAM on my MA876LL iMac7,1. Is it worth upgrading to 6GB? I also have a MB133LL MacBookPro4,1 also with 4GB of RAM and can be upgrade to 6GB. Is it worth upgrading as well? Are there any drawbacks in moving the RAM up to 6GB other than spending $150 worth of upgrades on 5yo Macs?