Most aircraft operate at a mach number above around FL300 and at IAS below that. Cruise mach number does vary depending on weight, winds etc. If you want something ask for it. That is in fact what most ATCO's do ! We generally fly at around M0.79/M0.80 on the 757 although this may be higher on occaisions up to M0.82 or lower 0.78 in turbulence. Below around Fl 300 (this FL may vary slightly) the IAS will be around 290 - 300 knots. If the profile is getting a little high the excess height may be traded for an increase in airspeed rather than using speedbrake unless the controller has asked for a specific speed in the descent.
I can assure you that co-operating with ATC is a vital part of our function at all times. That is particularly so when we are relying on those same controllers to help expedite our arrival as safely and efficiently as possibly. I am not sure how someone sounds "smug" over the radio but it sounds like you might have a personal issue worthy of addressing ?
The reason you are asked if there is any speed control over GWC or wherever is because it takes time to slow an airliner down and for planning purposes it is often very helpful to know this information in advance. Most pilots will be able to asses how busy the airspace is from the overall level of ATC chatter and not bother to ask, but simply comply with the speed restriction. If there is any doubt you may be asked, and of course ATC will often advise there is no restriction well before the aircraft reaches the speed limit.
We all know how busy ATC is, particularly in the London area, and we admire the effort and dedication that goes in to controlling aircraft so efficiently in what is a high pressure environment. I am a little shocked and dissapointed that you have laboured under the impression we seek to make your life difficult or set out to cause you trouble. such behaviour would be self defeating and generally unthinkable. Of course we would all like high speed unimpeeded access to the final approach fix. We all know that isn't going to happen unless it is very quiet indeed.
Remember also that the problems are not all yours. You "ATCO type people" will often spout twenty consecutive instructions without a break and then wonder why the backlog of aircraft all trying to establish handover check in, all step on one another. Of course we know this is just symptomatic of the high levels of traffic.
I dont know how long you have been doing the job but if it is a long time ( which I seriously doubt) can I suggest you book a holiday. If it is a short time then you might be interested to know that many airlines still offer a familiarisation jumpseat ride for the purpose of seeing the problems and operation from the other side of the fence. You might want to avail yourself of this facility. I think you would find it useful.