Yes 370' is quite a loop, and 4 degrees with no load is pretty respectable. Most boilers are recommended to NOT have regular return temps below 140f, as it reduces the possibility of creosote/rust forming. However, if you have a temperary drop of return temps below 140f you should be OK, since I only turn my pump on between OWB and FPHE when there is a call for heat (I get short 5-10 minute windows where return temps to boiler are below 140)
Question, you do have a CB so do you have the thermostatic bypass installed? Because if the supply temps from boiler drop low enough (the by-pass) will simply divert water back to boiler to be heated up to temp, before sending it out to radiant application.
**Good luck, if you do decide to go with a bigger pump (based on a quick check of a pump curve chart from TACO) it looks like a 0011 would be the next step up, from a 009. Just be careful you are not OVER-PUMPING the system, which causes noise and eventually erosion of metal fittings
EDIT: Added word NOT & below