That's a lot higher than I'd have expected. What is the normal stall speed in that configuration? What is the stall speed with the airplane with full flaps, slats extended, etc?
It varies significantly with weight and flap setting.
It isn't something we know. The applicable minimum maneuvering speeds are bugged on the airspeed indicators for each departure and arrival. On those with the updated software, or a flat-panel conversion, you get a series bugs that change with each change in flap setting. You'll see your current min-maneuvering speed as well as the max extension speed for the next flap setting in the normal flap schedule. On takeoff, you see bugs for the next scheduled flap retraction speed as well as your clean maneuvering speed.
With a heavy 767-300, I'm guessing (haven't flown one since 2013) that your clean maneuvering speed at max landing weight would be in the mid-230's with a Vref in the mid-140s with landing flaps. Fly the same airplane nearly empty and you'll see speeds that make you feel like you're going to fall out of the sky and like you're hovering on Final. The difference is that big.
I remember an approach in a nearly-empty 757-200 I flew to BDL. Approach kept telling the regional flight behind us to slow down, at one point telling him that he had "50 kts on the 757" he was following. I figured it was probably a CRJ-200, which has a relatively high approach speed due to it's lack of slats. After landing, I saw that it was actually a Dash-8 which is capable of very low landing speeds! Our Vref was 112 KIAS.
The 737s I fly now allow Flaps 1 and Flaps 5 at 250kts, Flaps 15 at 195 or 200, Flaps 30 at 165, 170, or 180, and Flaps 40 at 156/162/170/171 --Depending on which model. Rule of thumb is that you won't need flaps (due to maneuvering speed) until under 210 kts clean, 190 kts Flaps 5, and 170 kts flaps 15. You may need a little higher at very heavy weights. Generally higher numbers on the 767 at the lower flap settings. The highest Target speed (Vref + wind additive) I've had in the 737 was 165 KIAS.
All of that doesn't exactly answer your question but maybe it'll give you a ballpark idea.