been going back and forth on this for way too long. looking at a couple different 4inch frames for a light long range build, one has 3mm arms and one is 4mm. weight difference isnt massive but its there. ive seen people say 3mm is fine for a lighter 4inch and people say you'll regret it the first time you clip a tree. im not doing anything crazy aggressive, mostly cinewhoopish flying in open-ish areas with some light tree gaps thrown in. all up weight is probably going to be around 280-300g with the battery.

also partially considering the iFlight Nazgul Evoque F4 but its maybe slightly bigger footprint than i want. at that weight and size does the arm thickness thing even matter or am i just overthinking it because ive had two bad arm snaps on my 5inch and now im paranoid about everything

for a 280g build on a 4inch i genuinely wouldnt lose sleep over 3mm vs 4mm arms. the loads are just lower at that scale and if the layup quality is decent 3mm will handle normal freestyle and light crashes fine. where it really matters is like heavy 5inch builds with big motors hammering the airframe constantly, thats where you notice arm flex actually affecting flight characteristics. the paranoia from arm snaps is real but those were probably a diffrent class of impact than what a lighter long range 4inch usually sees.

idk man ive snapped 3mm arms on a 3inch before so i always go thicker when i can. but that was in some pretty dense wood with concrete paths everywhere, probably not comparable. the Nazgul Evoque is a solid frame though if youre considering it, ive put mine through a fair bit and the arm joints havent given me any grief. the weight tradeoff for the extra rigidity felt worth it to me personally but im also not optimizing for range the way it sounds like you are