First, thanks to whomever turned me on to the 42 tooth biopace ring.
I found one at Yellowjersey.
Because Shimano intended the 42 tooth biopace ring as an inner ring on a road bike, it has its chain ring bolt bevels on the "wrong" side.
I think because of the "wrong" sided bevels, this ring has more adjustment for position than the rings I would normally put on my crank star.
Using Sheldon Brown's chainring-centering method (I can't find a link to it right now), this new chainring centered up better than any of my other chainrings, round or biopace.
This, and the small size of the 42t biopace, let me adjust my chain much tighter than I could in the past, making for a significantly no-slack chain, round or biopace.
Using a KMC 810 chain and a 17t EAI cog, I have 64.9 gear inches and the quietest chain I have ever experienced.
Absolute total dead silence.
So I went out for a test ride on my regular 12.5 mile training loop.
This loop goes through rural, suburban and urban traffic with an up and down of about 1000 feet.
Actually, about two ups and downs of 1000 feet.
I have ridden this training loop regularly with both round and biopace rings, at 82 gear inches, 77 gear inches and 72 gear inches.
I have the same personal record of 53 minutes for this 12.5 mile and 1000 foot dynamic range training ride, at all three gear inches.
However, because of the dramatic drop in gear inches to 64.9, I expected the reduction in my top speed to significantly increase my time for my training loop.
During my ride, I seemed so much slower, especially on the downhills and flats, that I assumed a confirmation of my expectation of increased time.
Imagine my surprise when I completed my training route at my personal record of 53 minutes.
The same training ride, whether ridden at 64.9 gear inches, 72 gear inches, 77 gear inches or 82 gear inches takes the same amount of time: 53 minutes.
I think the hills have something to do with it, and I suspect the lower gear inches make for more consistent speeds, if not as fast on the flats and downhills.
Anyway, I noticed a dramatic improvement in control and agility at 64.9 gear inches, for the same average time.
I also noted a significant improvement in my ability to analyze my spin and consciously input changes, especially going over the top, from about 10 o'clock to 12 o'clock.
Placid Quiet's visualization of directing the knees towards the bars really helped in this regard, as did someone else's visualization of "scraping the bottom."
So, by gearing down, I have a better spin training tool, more control and agility, and, in the area in which I ride (with its hills), no penalty in overall time from one destination to the other.