Ok guys, thanks for the recommendations, I agree the XXL will flex more.
@Vince.Fab : I have already added support to the bottom center of the wasteboard to limit sag.
@Rich: Yeah I should have gone with the Makita instead…
Anyhow, Winston Moy recently posted a C3D video about cutting alu on a XL (with some recommended feeds and speeds). The machine seems to be doing well with the 102-Z endmill @ 10k rpm and 20IPM (which if I’m correct is a pretty decent chip load=0.008). He says that scaling the feedrate up 60% (for use with a DeWalt) works but it’s less forgiving for the endmill in case of mistakes. I think I will try some cuts with the dewalt @ 16k rpm and 30 IPM see how it goes, my work will be mostly plywood/wood and some alu but if things go well I will make more and more shiny stuff and I don’t want to waste endmills!