Both of Silman's books are good (I've even gone through the Reassess Your Chess Workbook) but they really didn't help my chess rating at all. I think that you'd need to be a Class A or Expert player to really get a boost in useable knowledge from those books. When I was trying to play Silman's way I'd get into really complex positional games, hold my own against strong players for 20-30 moves, and then miss a tactical shot or simply blunder. The book that really opened my eyes (and boosted my rating) is Rapid Chess Improvement by Michael de la Maza. He has a set of drills and a tactical study regimen that is a little too much for me right now (my wife and I are moving) but I've modified it to fit my limited free time and it has really helped me a lot.