MarkSF, I just happen to have the formula to calculate sheet loads.
((Maximum expected windspeed) ^2*(sail area in square feet))/232
When I plug in your 150 square feet and 25 kts wind speed, I get a load of 404 pounds which is well within the smaller block’s specs. To get to a thousand pounds of load, or half the block’s rated strength, you need to sail in 40kt breezes. No reason to “over kill”. Garhauer makes a pretty good block (ball bearings, etc), they are just a little “industrial” looking. They will be at the boat show and if you can wait, they usually have pretty good show prices. I had to google the Bristol 31.1 to get an idea of your rigging set-up and I saw an ad for one being sold in Alameda. Is that yours? If so, my boat is not to far from yours so PM me if you have any questions about the area. We’ve been sailing out of the Estuary for many, many years and love the close proximity to the Central Bay and the Ocean.