Radonaway GP fans are high suction low flow fans to be used with tight soil conditions. However, just because you think a difficult situation exists, it won't be truly evident until you put a hole in the floor. Then, an accurate assessment can be made of your soil conditions.
There's no sense buying the biggest fan only to find out that you could have used a 50 watt high flow model. If you want some help please go to the Radon Mitigation DIY page and fill out the form at bottom of the page