Wouldn't be too surprised if it was a blackbird. Used to see them alot round here. One was so low it shook the house one day! You are correct about them being somewhat bigger then the fighters, they were originally designed as a bomber!
http://www.sr-71.org/
Unofficially nicknamed the "Blackbird," the SR-71 was developed as a long-range strategic reconnaissance aircraft capable of flying at speeds over Mach 3.2 and at 85,000 feet. The first SR-71 to enter service was delivered in 1966 and due to politics, it was retired in 1990. However, the USAF still kept a few SR-71s in operation up until 1998, after a few were brought back to service in 1995. NASA's DFRC at Edwards AFB, CA flew the SR-71 from 1991 until the program was cancelled in late 2001. Visit the Blackbird Archive to learn more.