You will LOVE the Dragula! Looks great, sounds awesome, and has excellent performance. I run the S/C/S-4, which has straight headers instead of the stepped ones like the Dragula. This helps some with the low end torque. It also has a slightly different collector, but uses the same Dragula muffler.
Big 2-1 pipes like the Dragula are made for big, high-HP engines... and they are more focused on making power at mid- to high-RPM than they are at low-RPM torque. To make the most power from the Dragula, you really need to run higher duration cams, because the pipe is super-efficient at scavenging. If it empties out due to too-low exhaust duration, the power will suffer due to low exhaust gas velocity. The stock, low duration SE 255 cams will not play well with the Dragula, and you'll lose a lot of power with the stock SE heads. The components all need to work together, and low-duration cams with a big 2-1 pipe will not.
I was running Andrews 54H cams (238/238 duration) with the Fullsac setup, and they worked fine. But when I switched to the S/C/S-4, the power just wasn't there. After some research, I switched to the SE 259e cams, and they sound awesome and perform very well. Mean, angry sound when I blip the throttle, and the 246/250 duration is perfect to keep the big 2-1 pipe full and happy all the way to red line. Everyone in my riding group knows when I fire up the Honey Badger... it's pretty loud even just sitting there idling!
With bigger cams, you should also install a set of Cometic MLS .030" head gaskets, to help the squish. For the best performance, 10.5-1 pistons are really needed, too... big cams need high CR. That's a step that I haven't taken yet - but I plan to soon.
And with the Drago's pipe, you definitely need the left side ghost pipe. It will look really bad to have a big hole on the left side where the left muffler should be with your stretched bags. It's about $300, but it is an aesthetic "must have" on our FLHXSEs.
Ken