I feel it kind of depends on what the main purpose of this system is. Is it mostly going to be used for movies, games, music, or an equal mix? What is the size of the room this will be in? In my opinion, if you use it mostly for movies or games, the studio 20s will be fine. Now if you use it mostly for music, the beryllium tweeter should really shine.
Here is a review for the Signature S1v3
http://hometheaterreview.com/paradigm-signature-reference-s1-monitor-loudspeaker-reviewed/?page=1
Here is a review for the Studio 20v5
http://hometheaterreview.com/paradigm-reference-studio-20-v5-bookshelf-speaker-reviewed/
I currently use the Studio setup and I own 2 pairs of studio 20v5 that 1 set is my rear surround and my other set is my wides. I often debated the whole signature line verses the studio line. The reason I went with the Studios verses the Signature was two fold. First 90% of what I use the system for is games and movies. Second, the prices I got the Studios for were significantly less than the MFSP, which I got through stores closing out Paradigms. If I were to pay full MFSP then I probably would of went with the Signature line, just because of the tweeter and thicker cabinet. The sad thing is Paradigms are starting to leave the performance for value realm. The prices for the same versions have went up 30% since they were introduced and more people are finding more value for less from other manufacturers. Now understand these are just my opinions and take them as just that.
