A77+16-50mm F2.8 kit or A55+new CZ 24-70mm F2.8

Long time reader to DPReview, 1st time forum poster:
With the discounts on the A77, I'm debating whether I should upgrade to a new A77+16-50mm F2.8 kit or keep my trusty A55 and get a new CZ 24-70mm F2.8.

The overheating on the A55 during video recording is a bit annoying, but other than that, it's been a pleasure to use.  I currently have the Sony 18-250mm as my everyday lens.

Will I see a significant improvement in IQ if I switch to the CZ lens?  As I've read in many posts, glass matters!  The 18-250 seems very slow to focus so the CZ seems like a superb lens to have since I plan on keeping it forever.

Very tempted to upgrade to the A77 considering the sale ends on 1/26 so any advice will help tremendously.