I have tried them with both. Huge difference and it's very noticable.
You can run NiMH packs if you want to slow them down a bit, but I run the Losi 2S packs unregulated, and they blaze. You can even tell when your Lipo is getting low because they start acting like there running on NiMH packs. Thats how I judge when to change the battery on my rides.
I was running them with a DX3.0, and they were amazing. I just upgraded to the DX3R and WOW.. Now these servos really move.. I had to really re-learn to drive and get my reaction time caught up with how fast they are.
Either way you choose to run them they run great and are an awesome investment. I would take them even if they weren't HV servos just for the fact that the cases are full ALU and they will take a beating. No more breaking ears on servos in bad wrecks or front end chassis case on a mis-timed jump.