What e-mail - calendar porogram do you use?

I switched from Outlook 2007 as I was having issues with the way it worked with IMAP. I switched to Thunderbird 15.01 and am not happy with the way it uses my system CPU resources. It's using between 30 and 50%. I have the fastest and newest i5 CPU with 16 GB of memory and a SSD system drive, so it's not my system. I've looked around and don't see many options for other software. The reason I use IMAP and not POP is that I work from 5 different pc's and a smartphone and it's nice having all my PC's synched up with my sent e-mails. I also need a calendar program that sychs to the e-mail as well. I'm using 5 different e-mail accounts also for my different businesses which include G-Mail, Yahoo and 3 hosted e-mail addresses by Bluehost.com With Thunderbird, my system keeps saying the program is not responding. I downgraded to version 13 and then upgraded to 14 with the same results. This makes me kind of miss Outlook!

Gadgetman