FInd out what the billing requirements are at the firms you are interested in, that will tell you how many hours you have to work. A 2000 hour billing requirment is going to run you roughly 60-70 hours a week at work, depending on how much nonbilling stuff you do (like eat, development, firm meeting). 1500 is going to run you about a 40 hours a week, both assuming you take 2 weeks vacation and holidays.
Also just because you bill 2.5 on a project does not necessarily mean you will get credit for the full 2.5. A partner is going to approve the amount that will actually be billed. Different firms treat unrealized billables differently, thay may count for perfomrance reviews but not bonus requiremets.