Soliciting comments on my new training method

Comrades, This is my first post, thought I have been a Masters swimmer for about 11 years now. My question has to do with endurance training. I am primarily an open water swimmer, on lakes (smooth water). My speed is around 24-25 min/mile. I have what most people consider a very smooth, long stroke (~13 s/25yd). What I want is to increase my speed in the 1, 2 and 3 mile distances. I am self-coached, and seldom train with anyone else. Normally, my usual training is to just get in and swim. I used to go 3500 yds (2 mi) at a time (3 times/week), but I have pushed that up to 5300 (3 mi, 3 times/week) this spring. (I also run quite a bit). My new plan is to mix this up somewhat. I have been experimenting with what I call a "fartlek-pyramid". I warm up (~1000 yds), then do an continuous, ascending set of hard-easys, like this: 25h, 25e, 50h, 50e, 75h, 75e, ... up to 200, then descend the pyramid, 200h/e, 175h/e, 150h/e, and so on. (The hard laps are done at a speed just below stroke breakup). So, yesterday this gave me 1000 yd at medium speed (the warmup), plus 1600 hard and 1600 moderate/easy yards. So, anyone out there feel confident to tell me what they think of this? I feel pretty tired afterwards, which I interpret as a good sign that I am pushing myself. I don't like to stop and look at the clock, and I get bored looking for workouts on the web. This one is simple, and can be easily lengthened (just keep climbing the pyramid). It allows me to concentrate on my technique at various speeds. Any thoughts?