With the 105,000 PF now established, the 19/66 will more definitively rule the IDPA SSR roost. The 686, while near indestructible, is a tad heavy. The 15/67 standard earlier barrel config points really quick, but might (not yet sure) be a tad light compared to 19/66 handling.
The HB 64 you're thinking about could work, if you get the load regulated to shoot to point of exact aim in your particular gun.
As far as mod's go, OKFO's list happens to be nearly exactly the same as mine. I do put in a Brownell's action kit (ribbed, light mainspring) and go the 14 or 15# rebound. I'll take the DA pull down to near 7# since I'm going to run Federal primers.
I tend to run minimum fore-aft cylinder play to help make sure the Federals pop every time.
To get near a bobbed hammer, without cutting off the hammer spur, I like the stock service width hammers (.265) as opposed to the semi-target that comes standard on the 19/66/686 series.