I actually am a huge Rana fanatic myself. In order of importance / good results, here's my goals with gear/food/atma.
Weapon Base Damage (Apparently moreso than for Y/G/K) - Recommend Kikugosaku
Attack (unless you have over 800 with food, if so I suggest DA/TA as highest importance)
Double/Triple Attack
STR
Accuracy
If you have Shadow Gorget, Shadow/Anguinus/Sentry Belt and Champion's Galea, and capped GK skill, you generally will not have any problems consistently hitting all 3 hits. (with Aggressor up especially)
It seems to only spike to very high levels of damage when you have attack buffs up. Or when you double/triple attack. The fact that it can do upwards of 3500+ with only 100tp is what makes it desirable. (At least when you don't have Tachi: Fudo) Also its higher TP output can be useful for making that 5-hit build work when you just don't have enough Store TP gear on your non-haste slots.