UPDATE
I cooked a 7 lb bone-in turkey breast Sunday. In theory, I had read to cook at 275 for 30 minutes per lb. Filled both baskets to a little over capacity (cheap Royal Oak ridge briquets). Put lid on with all vents wide open, with charcoal still slightly flaming. Breast was close to room temp when I put it on. Temp was about 325 on the lid thermometer for the first 30 minutes or so. I wanted it to be about 275 (the temp I read to cook the turkey at), so I closed the top vent about halfway. BIG MISTAKE!!! Came out about 30 minutes later, and temp was down to 215 or so. Opened back wide, and it barely came up. Left it going for about another 45 minutes at 200 or so. Looking at the coals, they already looked like they were going out some, so I pulled the rack with the turkey off, poured more charcoal in, and pulled the baskets to the middle and used the gas starter. Basically started all over again. Temp held only at about 290 after that, but I was able to complete my cook, and it all turned out fine. I even cooked two 1.5 lb meat loaves after pulling the turkey breast off.
It's still frustrating me that the max temp with the vents wide open is 325, and I can't seem to keep it there (not a big deal in the above cook, but what if I want to cook something at 325? lol)
And what will happen when I try to cook something using the snake method at 225? I am afraid it will not hold that temp, since I am getting 275-325 with a lot of coals!