That makes for 1l solution.
I get better prints from negatives that are fully developed, and find underdeveloped negatives, especially when compensating development occurred, very difficult to print. Particularly portraits.
To the original poster, it sounds like you are getting results that you are OK with, but then you ask whether you think more fully developed negatives would benefit you.
I say you might, because that's how I like to print them, but I like really rich tonality with deep fat blacks and vibrant highlights. If you like more muted tones, you should probably stick to what you're doing. There are no rules for what you must do.
However, if you need to go to a #5 filter to get the zing you want from your prints, AND employ a split printing technique that definitely is most beneficial for high contrast negatives, then that suggests to me that you might want to try developing your negatives a bit longer as they seem under-developed.
Start small, add just a little, like 10% more. Give it a fair shake, and see how you like it. I very much doubt you will block up your highlights doing this, but if you do it's easy to revert, and at least then you will know.
Only you can fully answer the question, by trying it. Don't dismiss it until you try.