OK, small (really minor) code change to teh netflow reader library. One type declaration (declaring the return value from a READ-BYTE call as an (UNSIGNED-BYTE 8)) seems to knock teh speed down to "comparable with C".

; Evaluation took:
;   16.45 seconds of real time
;   10.88 seconds of user run time
;   1.52 seconds of system run time
;   39,267,241,128 CPU cycles
;   [Run times include 0.59 seconds GC run time]

Same test file as before, so we're down about 0.56 s on plain "chug through the file".