rather than 6.5's, is there a huge sopund difference?

 

IMO a 5-1/4" speaker is a mid-range only type of speaker. This is why typically most high quality 2-way home speakers will consist of a 6-1/2" woofer and a 1" tweeter. A 5-1/4" speaker is just too limited as to how low it's frequency response can go.

 

Yeah i def agree the 5 1/4"s dont do nearly as well overall. IF you can get 6 1/2"s do it. Match them all and i think you will be very happy