pentax 17-70 or 16-50

Hi fellow readers,

I have decided to buy a K7 next week.

Which lens should I buy.

I like either the 17-70 F4 of 16-50 F2.8

I realise that the later is more expensive. Is the 16-50 sharper with better colours / contrast ?

I welcome your thoughts on both lenses.

Thanks so much for your help / guidance.

Adam