From being sponsored for years by radio companies,Futaba,
Airtronics,KO & Multiplex.. I can tell you the response time
from radio company to radio company & radio model to
radio model is very big. Airtronics is by far the smoothest
built radios on the market from the early 80's to date. You
can call them slow if you like. I call them smooth. Futaba
is a little quicker. I call touchy. KO very close to Futaba IMO.
Multiplex is so dam fast you better not be making any
driving mistakes at all because it will bite you in the azz in
a blink. Multiplex is blistering/lightening fast, way faster
then you can think IMO.

Some Futaba models are quicker then others some
Airtronics models are faster then others,some KO models
are faster then others. Multiplex is blistering no matter
what model you have, they are just insanely stupid fast
IMO.

I have no track time on Spectrum radios at all because
I feel from what I see at tracks they have very bad
quality control issues.. I would never run Spectrum
radios if they gave them to me..But thats just my
opinion..

I feel you are feeling more the radio response then the
speed control response between the two cars your
driving.

You could also have a problem like this: Your buddies
motor has (NEVER) ran even slightly warm & yours has
been run hot a few times. So now your magnets your
weak & your motor feels very lazy through the whole
power band. Even one time running your brushless
motor hot cause's the motor to respond lazier then
before you ran it hot. If you run it hot twice your in
big trouble because the response of the brushless
motor goes in the toilet very quick. Your motor will
get lazier & lazier every run after that in a hurry in
some cases.

You could swap motors with your buddy & see if the
problem swaps cars. At that point you will at least
know it's not your motor. You could also then swap
your buddies radio to your car & yours to his, if your
problems switches to his car you know it's your radio.

PS: Back when I drove for Multiplex I could let other
racers drive my cars & most could not even get them
around the track the response was just way to fast
for them. Most had no idea there was faster radios
out there til they drove mine. I'm running Airtronics
now because I'm to old to deal with Multiplex's
blistering speed. Radios are all different & everyone
needs to find the one that suits their driving style IMO.

Good Luck & Enjoy your R/C racing