The problem is that 5 months of straight dieting is going to innevitably lead to a reduction of your RMR. 1 cheat meal per week is not going to stop that. I don't have anyone that is looking toi lose fat go longer than about 3-5 weeks straight without at least a weekend long refeed period, if not taking an entire week off at maintainence to reset.
Your body doesn't want to lose weight, and it makes adaptations to hypocaloric intake (insulin sensitivity, thyroid hormone output, leptin release, etc, etc) to combat weight loss. You have to periodically "reset" yourself in order to continue to lose. Increased protein can help, but there's really no reason to go much more than 1-1.25 grams/pound bodyweight. Conversely, while low carb can have an affect on weight loss, with the amount of exercise that you're doing, I see no reason for it (way too much, IMO).
The more you try to cut away, the more your body will respond to slow this down. I would suggest slowly increasing your calories back to maintainence (by about 10% daily increases in calories) and staying there for about a week. Your goal is not to gain weight in this time, but a pound or two is no big deal. You can do this during your next overcompensation period (and if you're not taking back-off weeks, you really should be), and then dropping cals back down by maybe 300-400/day. Lift heavy with reduced volume, with periodized fluctuations in intake and volume/intensity.
For more information, you can look at my article in this month's Men's Fitness on how to adapt your workouts for your goals, or Alwyn Cosgrove's "Human Inferno" article:
Good luck!