Eating 6-8 times/day?

I already know that eating 6-8 times/day is one of the most healthy things I can do for my body... and I already do eat that way. I generally stick around 2500-2800 calories a day (6'3", 204 lbs, 14% BF). Recently, I haven't been "trucking" as efficiently as possible, and I believe it's because I'm not eating enough. I work out, generally, twice a day, or about 10 times/week. Half the workouts tend to be high-intensity interval training (ever heard of crossfit?) and the other half is just basic lifting with some interval bike riding for 25 minutes at the end. With my weight, my BMR is about 2100 calories. Coupled with just daily movement and the exercising, I figure that I'm doing about 3500 calories a day towards the total, however, I feel like I'm losing out on some energy. What I want to know, from eating this 6-8 times per day, how fast is my metabolism sped up? We talking the equivalent of 100-200 calories? or more like 400-500? Should I be eating a little more? Thanks!