I have the same vibration at 2600rpm which is between 60-80kmph also I think it is coming from my redline sports air filter assembly

i have the same problem with my coupe at the same speeds but its comming from the left front and ive tried 3 different sets of wheels and still no solution but it only happens when im slowing down or just cruizing at the 60 - 70 k mark but mine runs twin webers and socked ram tubes so im not sure whats happening
beats me

maybe it is the extractors hitting on the idler arm? mine does this sometimes while deccelerating while going around a right bend

in my cse I can eliminate the engine parts as the cause. This is because at those speeds, even if I shift to neuntral and no accelerate, the car still has the same wobble. hmmmm

Blofly,You think your vibration is coming from your Air Filter????????

my '69 corolla wobbles at 30mph until 35 mph; it's the brake rotors.
one is just slightly warped causing a solid pedal and solid steering, but a higher speed wobble
check your brakes at a really low speed (less than 3mph) and see if you feel and uneven drag

oh ya;
when it's wobling, hold your speed mid-wobble and apply your brake pedal slowly until it changes (better or worse)

Hmmmm, interesting. My 1200 coupe has NO PROBLEMS with anything above 110 kph. I'm only jealous that your cars will actually GO that fast. Mine won't.