Helen,
If you like the Blade 3.0, you'll love the Blade III 4.0. It has more power than the Bullet 4.5 or Yoz 3.8. A very versatile kite, good for jumping, scudding, landboarding and buggying.
In general Blades are not rated as good buggy kites because of the lift they produce. The 4.0 does need a fair amount of wind before it starts lifting and when it does, it is a lot easier to handle than the 3.0.
Good alternatives might be race kites or intermediates. Real race kites (like Razors, Bora's,...) can be quite a handful compared to Bullets or Blades which are easier to fly.
Echoes of the latest generation of Centuries are not so positive, mainly because it is made of havier material (same as the Buster).
The Oxigen pro should be quite good : intermediate kite, i.e. fast but relatively stable and very high quality of materials (same as Nitro, water repellant and light nylon sail and kevlar bridles) and the price seems fair enough.
Chris