i am thinking of buying a blade2 4m and am wondering what wind i need to jump with?

Depends on your weight, for me, I wouldnt start in any less than about 25, but hey, Im 295 pounds and a bit crazy. Most people should be okay to start around 15mph.

Scoop

The smaller the kite, the more wind is required for jumping. Additionally, smaller kites in high wind fly very fast and often erratically causing a sudden burst - then release of power.

It is better to use a large kite in lighter wind (5m+ in 15mph-). This offers more stable lofting and gentler landings.

For more info, do a search on this forum for "small kites and jumping", "large kites" and "kite jumping".