I can only comment on the new Rio M, but if the Rio L is the same, only a bit longer and wider (and heavier @ 14.6 Kg) it will make a pretty good replacement for your '02/'03 Free Formula 198.
Here's the specs on the FF 198 from the '02 website archive:
Volume 198 liters
Length 280 cm
Width 90.0 cm
Tail 66.3 cm
Weight (DRAM) 10.1 kg
Here's the specs. for the 2008 Rio L (Large):
Volume: 215 liters
Length: 290 cm
Width: 85.0 cm
Tail; 67.2 cm
So, the new Rio L is a little longer, a little narrower, and 4 Kg. heavier.
I've sailed the '08 Rio M very powered up on a 6.6 m2 Sailworks NXslm race
sail and it was very similar to what I remember the early Free Formulas (GO shape
in a lighter DRAM construction) to be.
I also sailed the new Rio M a whole lot ( 3 days/5-6 hours/day) this past weekend at the Hatteras/Frisco Woods Windfest in light to very light winds with a 5.0 m2 Sailworks Retro Ripper 3 rig.
Had no problems staying upwind at all, even towing some "wayward" students back in from quite a ways offshore in pretty much offshore winds.
I think you'll find the new Rio L to be just what you need, even with the heavier weight.
The Rio's are all "Tufskin" construction, and very durable, hence the greater weight.
Hope this helps,
P.S. Since you are working on freestyle moves, I found the Rio M to be the easiest board I've ever sailed backwards. Frisco Woods being very shallow, I didn't want to drag the Rio out over all that shallow water.
Turn board around, beachstart normally, and presto...... I could sail out "fin first" in about 8" (20.3 cm) of water.
You are a bit heavier, but the Rio L is a bit floatier so I think you could sail in 8" of water as well.