uk_atco 535/brownstar
Manual of Air Traffic Services Part 1 [CAP 493] appendix E......Communications Technique and Standard Phraseology:
The correct phrase is "Resume Normal Speed".
Please don't confuse groundspeed readout with Indicated airspeed, rough guide is add 2% per thousand feet to get True airspeed, and don't forget the wind.......my buddies and I in Area Control will never give you traffic above the agreed speed without co-ordination.
Brownstar....the phrase "standard speed" is not an officially recognised instruction. To address your point b]....
Resume Normal speed means exactly that; you may fly any speed which your normal operation requires for that particular cicumstance, it means that there is no artificial speed restriction imposed by ATC for traffic separation or marshalling [sequencing] other than those published for various portions of the flight e.g. Speed Limit Point on a STAR, or speed limit specified in a clearance e.g. in a SID.