Rear Speaker replacement Options

[Scott]

My rear speakers came blown with the car when I bought it, so now I am thinking of replacing them with either Infinity or Pioneer speakers. Good Guys and Circuit City each said that my rears are 6 1/2 inches, but when I measured the actual speakers, they were about 5 inches, and the grill openings in the rear seat panels were only about 5 1/2 inches. Anything bigger did not look like it would fit. Will it really work to put in new 6 1/2 inch speakers? (I have a convertible with 6 speakers, 2 reg front, 2 tweeters, 2 back)

Also, the salesmen at the stores I went to said I would not get the same good sound out of new speakers without an amp or maybe even new deck. They also told me to replace all speakers at the same time as the deck. Is this true, or were they just trying to sell me? Do I really need to buy either of those extras? I want to spend under a hundred bucks and would be fine keeping my front speakers.

Thank you!