Thank you Tomo Pauk
And reading the data sheets, it confirms Warbirds claim of 285 mph top speed for the Blenheim Mk I. It doesn't give a speed for the fighter conversion, which carried the gun pack beneath the fuselage, and I would assume this would detract some speed, but not massively so.
So I'm assuming in daylight action its performance against either of the aforementioned bombers, fully laden, would be good, until they jettisoned their bombs, in which case it would struggle to close on the G4M and only gradually on the G3M.
However, operating at night, equipped with radar, it would have a clear advantage on speed, being able to close with either bomber, until it was spotted. Anything wrong with my supposition?
Regards
Fatboy Coxy