Hi Tim,
Long arms and legs suck, I have long arms too.
You can fill out your frame, just fix up your diet and get consistent with training.
However, I really don't see how will not compromise speed when holding extra bodyweight, especially in the limbs.
That's like trying to punch someone with a 3kg dumbbell in your hand, you will be slower, but will have more power.
Then again, if your strength increases proportionally, you may not lose much speed.
Sprinters are well built and have the maximum speed.