If going 16:1 or 12:1 I would suggest to use helical gears.
The reason is that 16/12 spurs have a weird tooth profile that tends to wear bevel gears much faster than 18/13 ratio gears, while helicals have dedicated bevel/spur gears for those particular ratios.
My Cyma Ak runs on:
BOB (box o' bits) 13:1 gearset, short stroked by 4 on release;
FPS high speed delayer;
FPS tappet plate, modified to set the timing;
Solink 35k Advanced Brushless motor (unibearing, so no arl needed);
Unmarked spring, probably a M100/M110 to stay below 1J;
Perun V3 Hybrid + Clicker;
Lonex gearbox shell + motor cage;
FPS 8mm solid bushings;
FPS piston body, metal rack;
FPS POM piston head;
FPS alu cylinder head (I generally prefer plastic cylinder heads, this is just for testing);
FPS cylinder (3/4 hole);
FPS 19.70 POM nozzle;
Begadi Nebo hop unit;
Maple Leaf Super Macaron 70°;
Prometheus 247x6.05 barrel;
This setup gives me 24/25ish RPS on a 7,4v and just about 35/36 on 11.1, very snappy and somewhat "quiet".
p.s. my barrel is shorter than the stock, I have removed the typical aksu flash hider and adapter. Stock barrel length is roughly 290/300mm iirc.
Keep in mind that these lists are a rough guideline, the wonderful world of airsoft tolerances may result in your parts not fitting together like mine or someone else's did.