If a bike has been recalibrated (tuned) for the airflow changed (a/c, exhaust, cams, heads, etc) through the system it will run great from the time it is fired up, thru warmup, and throughout the temperature variations, all the way to EITMS heat.
If a bike doesn't run this way the calibration is still off and it is not right to rely upon and expect the closed loop system to retune and save all the new values. It doesn't work that way so the bike's ECM will be working overtime to try to keep adjusting and readjusting values within working min and max values.
The purpose of the O2 sensors (closed loop operation) is to do minor trimming to fueling for differing fuel oxygen values (AFR) experienced out on the road NOT to recalculate (correct) VE values.
Hope this helps,
Bob

 

Stage 1 is supposed to be the most bang for the buck, not necessarily the most bang. So for HP improvement per dollar, stage 1 is pretty easy. Then you get into more expensive items like cams, followed by more displacement, etc.

The slip-ons do a little, but the cat is still pretty restrictive. Thus why HD doesn't require you to get your ECM flashed for slipons.

 

Cams are significantly cheaper than "stage 1" upgrades and provide much more of an increase. You can get the parts and do it yourself for about $400. Stage 1 upgrades aren't cheap and don't make a world of difference.