I've got two Outbacks and one has the ST fins, one has standard and I've got the turbo fins on the Pro Angler. I was against the turbo's on the Outbacks because for years the hull wouldn't handle the load. Now that I'm sure it will because of the redesign and strengthening, I'd not be a bit afraid of the turbo fins on the Outback. It makes for a very leisurely kick to maintain good cadence and speed. This also means the "hull tight" flutter kick will be somewhat more productive for leg motion. The PA needs the turbo fins just because of it's bulk. I think I can run away from my Pro Angler with the Outback if I had to in a long cruise. The PA certainly takes more effort for the endurance run than the Outback does. I'd venture to say that going out with other 12 foot kayaks, the Outback would easily wear them down after a while with the turbo fins. Of course if fishing and not running around, it doesn't matter. The ST fins do a decent job of perking up the Outback too. Gives a better feel of resistance but not too much. I'll put the PA turbo fins on the Outback and probably won't look back. Flutter kicking is the thing to practice though, like he said. It's kept my paddle in the holder most of it's existence. It's very smart to go with the ST fins and keep the standards as spares.... cuts the cost of having spares around. You won't be disappointed in the ST's. That should confuse you.

If I was to put some unscientific numbers to the issue, I'd say something silly like "probably .25 -.50 mph increase in
normal cadence" between the standard fins and turbo. The same cadence will get you further down the water. But it's not like a VW and a Corvette. You'll maintain your optimum cruising speed with a slower cadence and slightly more resistance.
The rudder..... I'm thinking they all need the larger rudder. Especially if you're wanting to sail at all. I've sailed the PA and I've had them all out in fairly rough water and following seas.... the rudder does come out of the water but I'm not sure the longer one would help much in that case. I've never considered needing the longer rudder on the outback. But I've considered changing to it because it's not that expensive a deal to do it. Just don't know that it's called for.
Oh crap... fishfinder... forgot. I rigged a mount to make use of the sail mount. To be honest, I quit taking the depth finder with me. I didn't find it all that useful in the waters I normally fish. If I was going to lakes and areas I hadn't been familiarized with, I'd take it along to figure out the bottom and structure.