To be technical, the hub method using 16g 25', connected to a 12g home run on your typical 25 amp circut breaker is not to code as I understand it. The circut breaker or fuse must be rated for the smaller wire used, unless the smaller wire is 12" or less from the fixuture to the 12g home run. If you fuse at the hub to the load of the fixtures then you are ok. I have found some hub method wired systems where there was a short in the 16g fixture wire that did not trip the tranformer fuse and turned into a cigarette lighter. We use 12g wire up to within 12" of the fixture on every job we do after I found that in 2 jobs and consulted several code experts. It is not worth the risk in MHO.
Tommy Herren, CLVLT #1169