Best I have heard at that price is the Orion P series available at onlinecarstereo.com
Most people will tell you that you will hear a night and day difference in midbass response by going up to 6.5" drivers.
However, with these new high excursion mids we have now, like the Orion's, you can drop the crossover point lower than normal, say from 80hz down to 60hz on the 5.25" drivers and get the midbass of the 6.5" with the better off-axis response of the smaller, less beamy 5.25" driver. The smaller driver is easier to install in many cases also.