Sorry, but I don't have MSP-IAH (don't often go between CO and NW in one trip, and I definitely have no plans to end up in IAH in the near future...)
Other IAH segments I have flown within the past year include:
SFO-IAH CO OP, posted to NW as 1,635
PIT-IAH CO OP, posted to NW as 1,117,
IAH-YYC CO OP, posted to NW as 1,747
IAH-TUS CO OP, posted to NW as 937
Hope that some of these datapoints help in your quest to figure out which system is reliable
