Not that I consider myself a lowballer by anyone's terms, but I swear 651 lasts longer outdoors than 751. I had to re-do a 751 job not that long ago, and I have a tanker with 651 that's been outdoors for 8 years on a construction job site, that looks primo, doesn't even show shrinkage.
Doesn't make sense, but I swear there's a little magic in 651.