For anyone that is interested, I did travel to China in July which was a fantastic experience. Beautiful country with fantastic food and some really beautiful cities and countryside, sadly let down by a lot of people (but that's another subject).
Just a note on the equipment, I had absolutely no problems at all. When I arrived in Pu Dong airport, Shanghai, customs didn't bother to check my baggage at all and through July I took quite a few flights and not once did anyone check the weight or the equipment I carried. The only time I got pulled up was when I accidentally put a pair of nail-clippers in my hand luggage. If anyone is interested in weights, I flew with Emirates and the total allowance was 27kg (1 checked and 1 hand luggage). When I left China my checked luggage was 28kg, hand 10kg. Quite a large amount over the limit and no-one bothered to check
One thing I did discover was carrying two mediums of camera equipment (ie film and digital) is a real pain in the ass. July was ridiculously hot and on occasion reached 45-49C and a couple times my partner, who is from Taiwan, said it was the hottest she had ever experienced. So my recommendation is if you are travelling in the summer, stick to one camera and 2 or 3 lenses but if you travel any other season, go for it with regards to equipment.
One other note which might interest people, buying camera equipment in mainland China is ridiculously expensive. For example, the price of a D2X body was around $6000 / £3000. Ouch!