I don't know anyone who had a chance to test both back to back but I know the different advantages in design of both. The rad valve uses some kind of separators to redirect and stabilise the flow for a symetrical distribution in the engine. Remember that the airboot makes a curve around the shock and the carb is at an angle before the manifold; so comes the need to realign the flow. Boyesen make alot of testing and they claim to make sure their product makes an improvement. I have heard people complaining that the rad-valve didn't make any improvements. The answer from a Boyesen rep was that the improvements were not necessarily felt by the butt dyno but were tested to give faster lap times and a better power delivery. Is that true? I don't know. I believe though that boyesen has brought up the rad valve as far as that conventional design can go. I know that the rad-valve has proven to be a good product. The thing is that Japan has been improving too.
The v-force has twice the reed area compared to a conventional reed cage. it does make a difference in the low-end responce that your butt dyno can tell, and does the same wonders on top. On a good engine such as a kx250 98-01, I hear alot of people saying that there is not much difference between stock, or v-force cage. On slower engines, like the 00cr125 the v-force is the clear winner. I think that v-force has come up with a technology breakthrough. I don't know if Boyesen will manage to improve still the conventional design. It's funny to think McGrath was using a v-force cage while he was sponsored by Boyesen? I think v-force has a better product but not enough to justify selling it twice as much as the rad-valve. In some cases, you may have more for your money with the rad-valve.