Generally a 6x8 or 6x9 should provide more bass than an equivalent 6.5" because of the increased cone area. A 6.5" component set generally has better sound quality which can normally attributed to better crossover components.
If you want a cheap, yet good set of components, go to
www.zalytron.com and get the Focal 129.00 component sets. The crossover needs to be assembled, but the mid and the tweet are very high quality. A couple people I know have used a generic 2 way crossover made by ultimate rather than assembling the crossovers.