It really is interesting to see what does and doesn't work on certain basses. I am seeing 2+2 and would likely say that is the most common mix when someone uses a mixed set. I used to see a lot of 3 of just about anything over 1 Spirocore, but there is a very good chance that was because that particular bass scene was heavily influenced by a few teachers who preached that gospel. Although it has been roughly 8 years since I was in 4ths, I did settle on Permanents the whole way across for a while before I made the switch, and it worked quite well for me. The advantage of a full set is you usually have the best chance of both feel and sound consistency from top to bottom. Even with strings that work well together you inevitably find a bit of a difference between one and the other, and that can mean slightly altering your attack or weight when making a string crossing to achieve the best results. In passages that involve repeated string crossings that problem can be more pronounced, but the reality is that you usually have to approach your G string a little different than your A string regardless to what company they are made by and what tuning system you are using.
The big advantage of a mixed set is that it can really help us achieve what we want out of an instrument. I like the Spirocores on the bottom because they are a bit brighter and clearer sounding which helps to give definition to a low C string, which is not an easy thing to achieve. On the top of my instrument, the high strings have way too much ZING for my personal taste, so something a little tamer works for me. Plenty of people are in a similar boat where they want a little brighter bottom end which is why we see a ton of bottom string Spirocores out there, but others really like the deep dark "pipe organ" tone they get out of a darker string on the bottom. It also really depends on what you do with the instrument and what kind of a sound you are looking for. Some people love fast decaying pizz, some love sustain. Some love that dark, chocolatey, organ pedal sound, others call that mud. There are some fantastic strings out there that work for a lot of people I do not use because they don't give me what I'm looking for. It can be difficult for some of us to really understand that concept though, that if I objectively dislike something, that does not mean it is bad, or not the right option for someone else.
I would like to try a few other strings on the bottom other than Spirocores. The final frontier for a lot of 5ths players is low G strings. Other than Spirocore, Obligatos, and a few custom string manufacturers who will make anything, there really aren't low G strings on the market. Many 5ths players use a Solo F# string tuned up, but considering the Solo F# tends to already have a fairly high tension because it is a solo string, tuning it up a semitone often chokes the instrument and really does not work. On some instruments that isn't an issue, on others, it borders on unplayable. Solo A's are occasionally similar where some instruments do not like the tension, but considering you are using a string designed to be your top string tuned to the pitch it is designed to be tuned at, that is a less common issue. There are quite a few low C/H strings on the market that work really well, and orchestral D's are not an issue, so it's just low G's that would really be a game changer for a lot of us. While 5ths is becoming more popular it is still a very small part of the market, and considering the Obligato set was very poorly received until Pirastro reworked it several times, I unfortunately do not see many string companies putting the resources into developing low G's in the near future. If enough of us got together, generated enough interest in one particular string such as the Flex Deluxe for example and said "if you make 25 prototypes we will buy all of them and give you constructive feedback on them" they might do it, but getting 25 5ths players together, let alone getting them all to agree on one particular string to prototype would be no small task.
