The one i used and is supposed to be the closest is the topscore cd. It is pretty good, but still not that accurate. I was getting 16s on the bio part and ended up with a 21 on the DAt, and getting 21's on the percpetual and enedd up with a 16 on the PAT!! But i guess a lot of it is also luck with the questions you get, and I studied for bio for an extra 4 days before taking the real thing.