I have an 07 FLHX myself and went 21" coming up on a year now. Yes I noticed a difference initially as it sits slightly higher...enough for me to notice as I ride and it handles slightly different. Nothing you wont get used to. After the first day I never noticed it again. I didnt need to adjust my front fender either for clearance and Im running an Avon.

 

I recently changed from the stock 17" on my 09 FLHC RK to a 21" front wheel. I noticed that there was a BIG change in the lean of the bike when you put it on its kickstand. I thought it was going to fall the first time I leaned it over. I installed the Progressive Lowering kit with drop-in springs and cut the pvc spacer to lower the bike 1". Made a huge difference with the lean angle. It's pretty much back to normal. However, I have also found that my highway bars across the front of the frame impact on the top of my fender if I hit a sudden sharp bump. I am considering lowering the fender slightly but I don't have much room to go down. Anyway, just something to consider when you're deciding what you want to do. Love the looks of the 21". Handles great.

 

I have a 21" front wheel and I have had 3 Harley's with 21" front wheels. Lower front end 1" and get a good tire and call it good! It will Ride and handle just fine. I did find if you do not lower the front 1" it does make the front end feel a lil heavier. You will be happy if done right.

 

Would lowering it 2" be to much? I have the same issue, 16" to 21".

 

On my 09 RK, I couldn't lower it 1" because my highway bars kept hitting the fender. I eventually had to insert a 2" length of PVC pipe (3/4" diameter) at the top of the lowering springs to keep it stock. Now it doesn't hit. There wasn't any room to lower the fender.

 

Might be easier to compare the overall diameter of your current wheel/tire and the 21". Divide by 2 if the 21" is the greater and that's the drop you need.

You may know this or someone can correct me, but the stock SG is a bit lower in the back anyway, so any front height increase will be that much more.