if it's warping with pla - it's not stuck to the bed well enough.

Try glue stick :-)

Can be a bastard to get prints off. So waht i tend to do is just heat the bed and you can usually wiggle a scraper underneath once it's softened a little.

And seriously 25% infill with plenty shells is just as strong as 40% - still a pretty dense matrix. But prints faster and shouldn't warp as much. Or at all if it's stuck to the bed properly :-)