I would also go with the Grundfos. Great prices on ebay for a 26-99. The one you have is pretty small for your distance anyway, I can only assume you heat load is either quite low or the delta quite high. 26-99 would be a more proper size
I'm not an HVAC or plumbing guy, so I'm not sure how to answer on the heat load. The house is 4000 sq. ft. and super insulated (R60 blown-cellulose attic, R20 dense-pack cellulose walls, R7.5 foam board wrapped around the entire house under the siding). We built in 2014. It's been heating the house and the 1200 sq. ft. detached garage (R50 blown-cellulose attic, R20 fiberglass batt walls), along with DMH, just fine. Does a super-insulated house equate to a low heat load?
Here we are January 24, and I still haven't purchased another pump. I tend to procrastinate. In fact, I once wanted to go to a seminar on how to stop procrastinating, but I kept putting off signing up for it until it was too late... ;-)