I was classically trained on the piano. The main problem is if you speed up or slow down the pitch of a sample you are changing the key or pitch of the sample which means you have to do the same to your synth. Any time I play over a sample the first thing I do is find the root key to the original sample in original time using a piano tone on my synth. Then I can speed up or slow down and chop the sample like I do normally. From there, since I know the original key, I can change the pitch on my synthesizer until the root key matches the sped up sample's pitch and tone.