This is an intriguing question, but I suspect that upgrading just the phono stage or just the cartridge will leave you wondering about how much improvement you will hear from upgrading both. It is also worth noting that the interconnects from your phono stage will also play a part. Based on my own journey, I suspect that the cartridge upgrade will produce an immediate benefit, but that a new phono stage should be the next move. Another idea is to try and demo a new phono stage in your system, as this will give you a sense of the change (and is obviously more practical than trying to "demo" a cartridge!) If you like the improvement, buy it, knowing that a new cartridge at a later date will only create further gains.
Best investment; cartridge or line stage?
Alrighty fellow hifi aficionados, I tried to find a sub on this topic but failed. Here is my bang for the buck question: assuming money spent on either option will be within spitting distance of each other, where am I likely to get more bang for my buck? By investing in a new line stage or investing in a new cartridge. I am currently running a Sutherland TX vibe line stage with a rega aria cartridge on a rega p6 turntable. Appreciate your input! Current system is McIntosh MA252 integrated, rega p6 tt and Martin Logan Vantages.