I am a firm believer in a fat and sassy EF, one that could effortlessly shout FU, only now I characterize it as "Opportunity Money". I had a career in comission sales, so I never lived on my current income. I also delayed funding retirement vehicles because I was saving for a DP. Sound familiar?
That said, for now, fuck the 6 mo. EF goal and stuff it into tax advantaged options such as H- or FSA, Roth, etc. Grab any matching funds that might be available to you. If you miss the window marked 2016, it's gone forever. Take advantage, even if it means another year or two to fully stock your EF.
Congratulations on the new house!
Oh, and I'm not a fan of prepaying low-interest mortgages , but understand the round numbers thing. Might I suggest $450?