After this training cycle is done I will max out at 65 lbs-20 reps on both abs and obliques using my lat pulldown, 6 times a week. Should I continue to increse the weight, but lower the reps? Or stay at this level?

I'd recommend trying some bodyweight exercises for your abs (crunches, reverse crunches, hanging leg raises, planks, etc.). Shoot for 200 total reps in any number of exericses/sets 2-3 times/week. There is no need to train your abdominal muscles as frequently as you are. Would you squat 6 times/week? Your abs are just another muscle group and should be trained accordingly.