Dennis, I will give this a shot...
The BK5 keybed took a bad rap initially from of all folks ..PSR users
The concensus being PSR's are the worst of any current keybeds..
The BK5 is not dramatically undersized..the keys have more width than PSR's (Actually only half inch in 5 octaves compared to the G70)..lenght overall of keys is 5 and 3/16 inch..about 1/4 inch shorter than Korg and Yamaha flagship models...and about 5/8" shorter than G70..
The keybed is solid on the BK..much better resisitance than the PSR's and Juno G..The throw is shorter than most , but the solidness of the action makes it more playable than most other low price beds..It is similar to the GW8, but just plays better..I think the previous Prelude did have a slight edge over the BK bed, but maybe the slight larger size may be the difference..
I have not liked any of the Korg keybeds..except the PA2x and 3x...The PA800 is only slightly better than the PA50 and following stuff..Korg should be ashamed to put a poor keybed on such an overpriced instrument as the PA800.
If you need to adjust to a lessor key feel..I think I would rather adjust to the BK5 keys over the others..If I were a piano player..I would not want to compromise beyond a G70 bed or PA 1,2,3x key feel..
For what the BK5 gives you in a small light package, and maybe the best drums of all the models...adjusting to BK5 key feel...is doable..