I don't understand this obsession with speed. I admit, in the beginning I too thought I had to be able to count down a deck while sitting at a stop light. (I still have a deck sitting in my drink holder.) But it is completely unnecessary. ACCURACY is what is important. You can always find a dealer dealing slower than molasses. (I always get them, even though I am now faster than any dealer I have met.)
Concentrate on getting the count right, and the speed will come. Until then, play against slow dealers.
Legal disclaimer: Nothing in this posting should be seen as endorsing or recommending counting cards while driving. Driving is too much of a distraction from accurate card counting.
Slow play is not good for winning at 21, so get up to a decent speed which shouldn't take too long. Try holding the deck with the cards face up. Riffle through them and you'll get to a point where you can do it in 30 seconds or less....and yes, accuracy is key. You'll get used to ignoring 3 to 5 cards at a time when they include neutral cards and values that cancel each other out.
"I don't understand this obsession with speed. ACCURACY is what is important."
Ye, accuracy is what is important. But think of the speed thing as exercise. Football players (in the old days I guess) would run around the field with tires roped to their waists---but not because they play a game that way! They become conditioned to run that much faster on game day.
When you are at home, without the distractions of a casino, and you don't have to look like you're not counting, you should be able to count much faster than when the money is on the line. That is (IMO) why one should care about speed. It is correlated with actual performance.
PS To answer the original question, I agree 35 is good enough for a beginner to go try things out in a casino (and realize how different it is than a kitchen table).