"Anthem x 2009"
If it were me (about the same weight) I'd be deciding between crest or arch EX, just depends if you really want the stiffness. If you're on QR forks for eg I'd be looking at crests
"seriously. theres only a few grams in it"
790-800g/pair or 980g/pair? rotating weight as well, so its hardly just a few grams
Stans Claim the BST2 make the 21mm internal arch EX (and crest) make it equivalent to about 25mm with a standard rim wall
"flows aren't the toughest rims as it is! can't see the Arch's holding up to too many cases"
Going from XM719's to Arch EX's one of the most noticeable things for me is how I've gone from a serial rim dinger and pinchflatter even with DH tubes and 30psi+ on the tall-rim-walled mavic's to virtually never rim dinging on the ArchEX's. The BST2 means its not pinching the tyre the same, so my rim walls are still good where the tougher mavics have had to have the adjustable spanner treatment a good many times
"Which out of the arch or flow ex is comparable to XM719's?"
Neither, I think all stans rims right down to the XC race ones are wider than 719's. Flow and FlowEX are similar weights. Not sure on toughness to rim ding's though
"non-tubeless maxxis seat ok then explode dramatically on the smallest drop"
With the Arch EX with the BST2 they might be awful to seat (compressor job for me) I never had them burp in the alps.
Also a cursory skim-read of that pinkbike article has me thinking their 'theories' (okay I only really looked at the pictures), don't apply the same to Stans, the low rim wall height on a stans mean it doesn't pinch the tyre quite the same as the pinkbike diagrams
"but do you need to add rim strips to the Stan's so might not be too much in it"
Only on older Stans Rims? Flow, Arch, 355 etc
Newer Crest, ArchEX, FlowEX just need tape (lighter than a rim strip for tubes) and a valve