Chip:
Well why the Hell wouldn't Merion be precisely as you described---they have bought into THE IDEAL MAINTENANCE MELD----BIGTIME!!
Mayday;
Green surface firmness and green speed are basically two different animals and as such they effect basically two different areas of playability, although naturally there is some overlap.
Green surface firmness primarily affects approach and recovery shots and the ability of a golfer to control the ball once it hits the green surface.
Green speed primarily affects putting.
Greens can be extremely fast but soft and a golfer can contol his ball well on approach and a green can be slow but extremely firm and a golfer will not be able to control his ball well on approach.
Obviously when greens are both firm AND fast the challenge of playing to them, around them and on then increases and sometimes exponentially.
"Ball Creep" basically has to do with putting and is a phenomenon that kicks in exponentially when green speed gets near 11 on the stimp and above.
A stimpmeter does not know and cannot tell if a putting green is firm or soft, it only measures the speed a ball travels across it. Greens can be 13 and soft or 7 and firm or any other combination thereof.
But the green's firmness does not directly effect greenspeed.