It is quite normal that the tiptanks are breaking off during the landing, this happens to most Radjets I know.
Theoreticaly, the winglets should improve top speed, but this will be hardly meassureable. But they improve noticable the high alpha capacity and make him more stable.
You can read a review on my homepage about the radjet: http://modelflying.weebly.com/radjet-800.html
I can't believe 200mph, mine goes 150mph (meassured) and without really big modifications it is not possible to go much beyound that. What setup (motor, batterie, prop) are you useing? The radjet looks much faster then he really is...
I'll look forward to hear from you and if you notice a change in the flight characteristics.