100-300 or 75-300?

Thank you all for your help with this.

Having read many reviews, both professional and consumer, it seems that the 75-300 is a little sharper at the long end, plus it has a somewhat better autofocus.

I do get the feeling that there may be a quality control issues (some less good copies out there). The 100-300 mention on Luminous Landscape talking of considerable CA seems completely at variance with other reviews.

Further, 5.6 to 6.7 is only 1/2 stop, so not too great an issue. The point that the 75-300 is no longer in production had escaped me, will a new version be produced and at what price will it be sold?