This type of discussion will always leave room for personal taste. Part of my affection for the P80 includes the price, size, weight, feel, etc...... it's the whole package. As for the K2600 - I'm NOT a fan. The RD600 seems a little dated to me. In the acoustic world....which is better:
Steinway or Bosendorffer ?
Shimmel or Baldwin?
No one can answer these questions because there are too many acoustic properties that will vary from piece to piece. That is why each manufacturer tries to get as many of the fine nuances as they can. Take all of our suggestions, and formulate your own opinion. The best tool is your ears - use 'em!

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Uncle Dave