Tim, first of all, you shouldn't have any problem with the base metal at the temperatures referenced. Secondly, js55 gives great advice and further, if you have access to an ASME Section VIII, Division 2, there is some excellent information regarding austenitic filler metals exempted from impact testing at very low temperatures. Of course, this isn't to say you would be exempted in your instance but if you look at the filler materials mentioned they are provided exemption because in most instances they have ultra low temperature characteristics which yield impacts as nearly meaningless. One example, while it may or may not work in your case would be ERNiCrMo-3 (just an example!).
An exerpt:
(2) For austenitic weld metal:
(a) having a carbon content not exceeding 0.10% and produced with filler metals conforming to SFA-5.4, SFA-5.9, SFA-5.11, SFA-5.14, and SFA-5.22 at MDMTs of -155°F (-I04°C) and warmer; etc.