You have two totally different problems to address.
One is neutral monitoring for testing rigs and making sure they will translate well to as many live situations as possible.
The other is getting a monitor sound that works for you personally on stage.
They are totally independent of each other. While it is tempting to think that the best solution for on stage is very flat/neutral IEM, this isn’t necessarily true. You shouldn’t care whether the IEM are flat and sound like the FOH mix. You only need them to sound good to you.
IEM are no different than wedge stage monitors. Many of the best hi end wedges are far from flat but have a peak in the range that accentuates vocals and makes it easier for the vocalist to be heard on stage. Unfortunately, that same peak can make guitars sound grating.
For IEM, I use Shure SE425 with custom moulded sleeves. They aren’t the best IEM out there by any stretch of the imagination but they are very detailed in the mid range where the guitar sits so they make it easy for me to get a monitor mix that lets me hear guitar well. A more neutral IEM doesn’t always sound better. In the same way as an EVM12L isn’t necessarily better than a V30 - they just sound different and some people like one more than the other on stage.
What does REALLY matter though is fit. Regardless of which brand or model you go for make sure you get them fitted to your own ears rather than using the little rubber or foam seals that come with most lower to mid range models.