On the contrary I do understand my adjacent sectors very well. And you're right, that is absolutely essential in providing a good service.
Perhaps my understanding of the mach/IAS is not quite correct then.
. . .
. . .Since at high level he is highly unlikely to be flying faster than 270kts, the speed restriction wouldn't really kick in until he is at say FL350(ish) (if flying at M0.85 that is approximately where I'd expect it to be). Bare in mind I never asked the pilot his mach number to begin with as I couldn't care less. I just needed him slower below FL300 as he descends and meets other traffic.
You were the one who said (Post 41) you didn't necessarily understand operations in other sectors...
Your understanding is essentially correct, but with a major bad assumption: IAS can well be above 270 at higher altitudes (the 747 frequently will cruise at 310 at M.85), so you SHOULD care about the cruise speed/Mach. If you want a specific speed at a specific altitude, then make it perfectly clear by stating "270 KIAS by FL300"! Otherwise, you will be at the mercy of the current FMS setting and a possibly lower switchover altitude.