never ridden the toxin, but i've ridden my aorta for year and a half before i got my dob, feels great, and most people thats ridden it said my set up was near enough perfect for the geo.
no cracks on mine, probably the only 1 to be honest, i've heard many of them cracking at the rear drop outs.
as for frame flex there's a bit so at least a 2 bolt booster is recommended, i had a 74kingz 1 (freaking beasty) it was really good.
the aorta shares the same geometry as the ZHI Z2, 1075, 380, +30, 72ha. which many people had said the geo is spot on between street and natural.
im about 5ft9, shortish legs and the bike seem to suit me alright, being quite biased i'd give the aorta ago, possibly a ZHI Z2
steve