Will Harley Stage 1 slip on pipes increase performance on a 2010 FXDC without out any other modifications? How about acceleration off the line?
It will help a bit but nothing drastic by themselves. If you do the air cleaner stage 1 and the slipons with some added fuel, you could see 10-12 HP and TQ increases.
Probably not noticably, but as Glider suggested, you'll love the sound compared to what you have now!!