Hi,
I'm 99,99% sure that, after returning to my secret "hobby-laboratory", I only changed the Programmer under the "Tools" menu and I have pressed the upload-button (the one with arrow draw on it).
All other selections was:
Board = Arduino Pro or Pro mini
Processor = ATMega328 (3.3V, 8 Mhz)
Port = /dev/ttyUSB0
I will try to make another test in the weekend (if my family allows that) and to post here the screenshots of the used IDE-configurations.
IMPORTANT!
Exactly in this moment, I'm making my experiments in programming the Pro Mini with the USBasp.
I can confirm you that pressing the upload-button or selecting Sketch -> Upload Using Programmer are doing the same thing/action when "USBasp" is selected as programmer.
Note: the downloaded sketch size was around 29K, more than enough to be accommodated in the standard Pro mini with 2K bootloader size.