I have 2 170's ( old SV's) and 5 140's ( 2 SV and 3 STI's) that I carry to matches. I own a couple of 140's with stock STI springs, followers, and plastic spacers that aren't reliable and will stay in the safe til they can be tuned and have the guts replaced.
For almost any match, I start with either an SV 140 or 170 in the gun, the opposite in mag pouch 1, the back up 170 in pouch 2 and the other SV 140 in pouch 3; I use one of the STI's in my back pocket for a loader mag.
These are the only 5 mags I use with regularity and honestly most rounds are fired out of the two 170's and 140 #1.
I rotate which 170 is used from one stage to the next. I will rotate the 140s also and occasionaly use the STI loader.
The only real exception is one of those classifiers with 2 strings and two reload.
I doubt if I drop the 170's more than once or twice a year and they always work.
If you only want to buy 4 mags get 2 170's and 2 140's. You can also use the back 140 as the loader.
My 2 cents.
Robert
L2723