Hi BlakesHitch--
The Fly will do fine for the SRT climbing we'll be doing at the Rendezvous.
You have your choice for how you secure your rope. We usually use a choker on the anchor branch. That way when you're ready to come down, you can untie the rope and bend it at its center over the branch, and descend on two. Then you can just pull it out of the tree from the ground.
With a 150' rope, you'll be limited to trees that have an anchor branch no higher than 75' up. Most of our SRT trees do. You can climb higher in such trees by resetting your rope and making the climb in several pitches. Then you'd descend in several pitches, too. Of course, you'll need a secondary safety lanyard (like New Tribe's Monkeytail) to tie in while you're moving your rope.
With your 200' rope, you can get into trees having a lowest anchor branch up to 100' from the ground. This means you may have access to trees your shorter rope couldn't reach. It also means you may have fewer pitches to your climb. Your throwline will have to be at least as long as your rope to take advantage of the additional rope length on the first pitch.
Most of the recreational climbs we've done in the past 15 years here in Oregon have been with 150' of rope.
Hope this info helps!
Sophia