In my experience the cheap chinese ball bearings lasts between 2-4 years. A lot depends on the load and speed. Since the blower bearings are somewhat of a pain to change, I would go with a good bearing. I classify the bearings I buy as Premium, good, and finally mediocre or worse. Premium bearings are NTN, and then SKF. Good is Nachi and Peer. Everything else is mediocre (NSK) or worse (RB Tech, etc).
In the high speed spindles that I rebuild, I only use NTN bearings. SKF bearings don't cut it in high speed service. I have been rebuilding high speed spindles for about 6 years or so now. To date I have not had one come back. (I offer a limited lifetime warranty).
When it comes to oddball bearings like the 1641, I try to get Nachi or NTN bearings. For something like trailing wheels, I will use RB Tech.
The reason the 1641 is so expensive is that there is little demand for it. I expect that one day the 1641 will no longer be made by any of the bigger bearing manufacturers. It will be like the 88000 (felt sealed) series bearings. There are no good 88000 bearing made anymore. They are all mediocre to poor.
I spent over $3000 buying ball bearings during 2010. The previous year I spent about $1500. I have no idea what I spent in 2011. Almost none of that money was spent on Gravely bearings.
When it comes to bearing life, I have not seen one good sealed bearing that was still good when it reached it's 20th birthday. Oil lubricated bearings like the bearings in the gravely transmission seem to last almost forever.
When I changed my blower bearings, both were on the verge of failing. Both were slightly rough. I replaced them both. The blower was quieter after the bearing change.
In general, when it comes to ball bearings, you get what you pay for.