Blotchiness and artifacts sound more like ink limiting issue but it could be just incomparable media.
The two RIPs here that I can run the L25500 on are Colorgate and Fiery XF. Colorgate has better control of the light inks but that is about all I can say for it. The main RIP I use is the Fiery XF and now at version 5 it does a better job of controlling the inks. Even though v5 it has the same limited dialog for light inks it controls them much better. But color is just better with the Fiery XF and the spot colors are so right on that I very rarely have to input lab values to get correct spot colors. The other printers I run with the XF I can say the same thing about and version 5 now uses the Fiery Color Profiler Suite version 4 which does a great job and allows me to do a lot of adjustments the black curve of the media profile for the L25500. This is an additional benefit if I want to reduce peppering in the highlights. I also use i1Profiler as well as it give me a lot of control over profiles and I like it for profiling media for printer drivers, RGB drivers in the XF RIP and also the Digtial Press
paper stock.
I have used and tested a lot of RIPs over the years including ONYX a few years ago (before I had a L25500) for our Gerber flatbed but I wasn't not anymore impressed with it than Flexi which we ran the Gerber with at that time. ONYX could have improved a lot since then. The only RIP that I would still like to really test out is Caldera. I have the trial but can't really test the whole CM process with the trial.
I have to admit I am just spoiled with the Fiery RIPs and there server/client setup where I can setup and print jobs with any
computer here. I use the Fiery EX on our digital press.