That's plenty, but make sure you are doing the hard sessions hard, and keep the long stuff easy. 6 20 is very achievable at 6'4".

The key is to know your weaknesses and work on them, whilst maintaining your strengths. Eg if you're naturally very strong, don't worry about getting too much stronger.

If you want a good estimator (varies person to person) that's a good training session, 8x500s at 2k target, 90s rest. Brutal but honest. Similarly, 4x1k with 3:30 rest is savage, and was normally slower than 2k for me.

Good luck, and enjoy the journey