It depends on what mix of Perkins and Stafford loans (or other loans you have)
Calculate the consolidation rate (it is the weighted average of all your loans...Perkins loans are 5%, Stafford loans vary depending on if they are in repayment or not). Then calculate how much interest you will pay for the life of the consolidated loan.
Then do the same without the Perkins and calculate the total interest for all consolidated loans + Perkins loans interest.
Do whichever leads to less interest being paid.
If this doesn't make sense, feel free to PM me your loan amounts and I can calculate it out for you. Or, ask your financial aid office to do this. They should be able to help you out.