Kurzweil developments over the last 10 years - PC3K to PC4 ??

Hi there
I was asking about the (lack of) digital outs in the new Kurzweil keyboards - but actually what I'm really trying to evaluate is the wider question of the features available on the new PC4 relative to the older (but not that old) PC3K.
The reason I'm asking is that I really love the Kurzweil workstations - they kind of seem to get the workstation thing correct to me, and the last of the PC3Ks are still available at now bargain basement prices.
So I'm wondering what can't they (the PC3s) do that the PC4 does?
Clearly the PC4 has "more" (voices, ROM, RAM) etc. - color screen (is that a big deal, I think probably not?) - but has there been some major upgrade to the whole package with moving to Kurzweil's OS4 - I'm thinking about the capabilities of VAST - the sequencer etc. etc.
(I know that FM is a big deal - but is that basically it?)
.... and here's the problem - while the PC3K is a beauty - top of the line instrument, the PC4 is down-right ugly .... I'm sure that one could get used to it - but compare the 2 side by side and there is no comparison.
...and yes, I can't actually compare them side by side because music stores don't exist anymore.
Any thoughts?
I was asking about the (lack of) digital outs in the new Kurzweil keyboards - but actually what I'm really trying to evaluate is the wider question of the features available on the new PC4 relative to the older (but not that old) PC3K.
The reason I'm asking is that I really love the Kurzweil workstations - they kind of seem to get the workstation thing correct to me, and the last of the PC3Ks are still available at now bargain basement prices.
So I'm wondering what can't they (the PC3s) do that the PC4 does?
Clearly the PC4 has "more" (voices, ROM, RAM) etc. - color screen (is that a big deal, I think probably not?) - but has there been some major upgrade to the whole package with moving to Kurzweil's OS4 - I'm thinking about the capabilities of VAST - the sequencer etc. etc.
(I know that FM is a big deal - but is that basically it?)
.... and here's the problem - while the PC3K is a beauty - top of the line instrument, the PC4 is down-right ugly .... I'm sure that one could get used to it - but compare the 2 side by side and there is no comparison.
...and yes, I can't actually compare them side by side because music stores don't exist anymore.
Any thoughts?