We have updated to 4.2.6 and it is great! The performance is so much better than it ever has been on the Pixelmon side. It also seems the next update for Pixelmon will be for Minecraft 1.9 which will be even better performance.
When that time does come, do not worry, no data will be lost. We will not be doing a new map. (Most likely ever lol!)
I do know that the next update will be and update and not a bunch of bug fixes.
If you are not yet, please use the Pixelmon Launcher, (I would download the beta version.) Under the PixPack section if you scroll down halfway you will see our PixPack there. It makes for very easy new installs and updates as it does everything for you.
Thanks guys and enjoy the update!