Introducing LED light into the setup is going to make your data hard to compare to anything else out there. And have a look at the LED grow journals--most people are using supplementary light at some point.

I'd consider a four foot, four tube Tek Lite T5-HO. At around $350 - $380 that's in the neighborhood of what you said you expected to spend on five sites w/LED, and you should be able to fit five buckets side to side under a four foot fixture (assuming the buckets are about 10" across each.) The Tek Lites are known to give good results.

Too many experimental factors make for a mess.