I used 3.5mm for the chassis and shock towers of
my project and 2mm for everything else, subjectively the 3.5mm seems about as strong as the 3mm 7075 it replaced but significantly lighter.
Hot Bodies Lightning 2 Pro carbon, Mega 22/30/2, MMM, 4s3-5Ah.
Tamiya F201 carbon, Mamba 7700, MM, 2s A123 2.3ah.
Xray XT8, 1518, MMM, 4s5Ah.
Lots of boats.
fastelectrics.net