I wear the same size in 4.3 as I did in 3.3. The 4.3 are a little wider as the upper is far more flexible and the laces are set a lot further apart. Some people did need to size down, but not me.
Overall the 4.3 has all the benefits of the 3.3 but is lighter, far comfier and better breathability. As regards comfort, it's the about the comfiest tennis shoe I've worn.
Only downside is that some have found the lacing system even more prone to failure than the 3.3.
Yonex E-Zone Xi100 - Tournagrip XL - Adidas Barricades - Nike Tennis Socks