The MRF24J40MB gives me > 2000 meters of range; no problem at all.
But it has to be line of sight (no obstructions).
See here: http://nerdfever.com/?p=1457
Here is a graph of LQI and RSSI against range (in feet) that I measured in practice:
Both RSSI and LQI are scaled to the range (0...10000). This is the very last graph from this blog post: http://nerdfever.com/?p=1552
Note that the distance scale (the y-axis, in feet) is ONLY vertical; I was just measuring altitude, not distance. The rocket (carrying the MRF24J40MB) landed ~ 1 km from the launch site (crashed, actually; see the post), so the actual distance is greater. And there were no obstructions; just air. Launch (T=0) was from a horizontal distance of about 30 meters.
Also, note the two data dropouts around T=13 and T=25 seconds. The range was pretty large then (over 2 km) and I did not control the relative orientation of the antennas - one antenna was fixed (on the ground) the other was uncontrolled. I think the gaps are when the antenna's radiation patterns were (by chance) in a particularly bad misalignment. This shouldn't be a problem for you unless you can't control the antenna orientation.
If you need more range between fixed points, you could also make a simple corner reflector to get a little more gain.
post edited by dlindbergh - 2012/03/03 08:04:21