Hi Martin,
As you know the level will be a lot higher than in the October and November which is when most kayakers like to go to the Zam. However, the July level is my favourite, the water is a bigger and scarier and the eddy lines do become a bot more of a worry. But for a solid class IV paddler you shouldn't have any problems, you ust just be made aware of some nasty spots like the Patella's gap in #7, which is running at that level.
The Zam is the he southern hemisphere, so July is midwinter (although it will be warmer than europe the cold may catch you by surprise). This means that the mosquitoes will not be much of a problem but take anit-malaria as a precaution.
I recommend you you fly to Johannesburg and then to Livingstone, alternatively you can fly to Lusaka and then bus to Livingstone but that is long and uncomfortable and not all together safe.
For more info and to organise your trip get in contact with Sven from
www.thezambezi.com.
Hope this helps
Scotty