Thanks all, and yes the maxi balls are a conical but the ones I have aren't prelubed. Pretty sure those are what I used last time with 90 grains. I should be good to go I think.
Kirk, as someone has already suggested the twist rate is a big key. If your Penn is a slow twist rifle for round balls you will have a problem shooting longer projectiles - especially if you shot them with to much powder.
So to switch to a sabot and projectile would be difficult because of the length of the project. I do not think you could get it to stabilize.
Switching to a short lead conical could work very well for you.
You could lube those maxi's with a little bore butter in the grooves also if you want to. But at the velocity that you will probably shoot them it really isn't necessary.