Cannondale Caad8 2013 Headset

Hi all,

So I have been road cycling 2 years now and using my cannondale caad8 through winter and summer.
Recently my headset has started to give a little play and a very slight gritty feel when turning the bars unweighted.
Sounds like a new headset if I’m correct? Problem is I’m struggling to understand which headset I need.

Here is my research so far…

Referring the the cane creek headset finder it stated I needed:
Upper:
IS 41 / 28.6
Lower:
IS 41 / 30

Discussing with Evans cycles they suggested:
IS42 headset 28.6mm upper and 30mm lower

And numerous people on different forum posts have suggested a campy 45/45 1 1/8 headset such as:
http://www.wiggle.co.uk/fsa-orbit-ce-black-1-18-integrated-aheadset/?lang=en&curr=GBP&dest=1&sku=5360398723&ci_src=18615224&ci_sku=5360398723uk&utm_source=google&utm_term&utm_campaign=Components&utm_medium=base&utm_content=slmFEN10M_dm%7Cpcrid%7C54887834342%7Cpkw%7C%7Cpmt%7C%7Cprd%7C5360398723uk

So I have come to the conclusion that 30mm being 1 1/8 the wiggle link would be suitable, however why is the upper slightly smaller? Does this require a specific set of bearings?

If anyone could suggest a suitable headset and help me understand why it is suitable I would be very grateful.

Many thanks,