Vince: Hmmm... I'll give you my impression with the hope that others will join in here also. Matching drivers, depending upon who you talk to, plays a more or less significant role. I read somewhere that NHT matches drivers in their 3.3 line to within 1.5 db of one another. I have a set of Atlantic Technology speakers. When I was talking with the tech folks there, the fellow mentioned that each speaker must perform within 3db of the final prototype or they don't pass THX certification. Northcreek kits match drivers to within 0.5% and crossover components to 1%. BESL kits do the same matching by tweaking crossover components.
Drawing out the common points from above, it appears that as the speakers become more expensive in price, the drivers are matched to increasingly tighter tolerances. The matching is easier if you purchase from places the sell kits because they have lots of stock to choose from and matching is easy. For folks like us, matching can become very difficult (and expensive) to perform.
So, to get back to your question, I'd say that +/- 10% in cabinet volume might just outweigh and cover over the differences in matching drivers. These differences can be manipulated pretty easily by adding/removing stuffing to your box, chaning the port lenght slighly, adding a flare to the port (if ported), etc. I know many people who spend a good deal of time tweaking the box stuffing and porting once they have finished a speaker.
