All workstations let you edit the patches. The main thing about workstations is not the editing (of which you can get from a synth). The main thing is on-board sequencing. You said you need a workstation with editing, but you still haven't pointed out the purpose of getting the keyboard. I'm asking this because you mentioned both workstation
and synth; so I'm picking on words to hopefully help broaden your choices.

May also affect your budget.
The criteria you need to consider before making a comparison (and then a decision) are:
1. What you need the keyboard for. If it's live performance with a band, consider a synth. If it's live performance and you are mainly a pianist (and use the standard bread and butter keyboard sounds), consider a stage piano. If it's music production/performing without a band, consider a workstation. If it's music production in a studio and not so much in a live situation, consider software DAW sequencing. etc etc.
2. The sound you need (dependent on the genre you intend to play/produce). This will not only affect the brand name (each manufacturer is inherently different in the strength of the type of sounds they produce for different genres), it will also affect the kind of control you need for sound manipulation (do you need faders/knobs/mod wheels/aftertouch, do you need live editing of the sound and how deep).
3. The others stuff - touch (are you playing mainly piano sounds and so need an 88 key with good weighted action, or are you playing mainly synth sounds of which the touch isn't as important? - note workstations come in both weighted and non-weighted versions as well), the number of keys, etc.
4. Budget.
Both the M50 and the PC3LE do sequencing. All workstations let you edit patches. M50 lets you edit the patches deeper; the PC3LE is a "lite" version of the PC3 - main difference is the "deepness" of the editing. (it's therefore fairer to compare the M50 with the PC3 instead of the PC3LE). The sounds are very different. As you noted, the touch is different. In other words, they are pretty different! To make the decision depends on the decision tree stated above.
If you are familiar with the Korg, I believe you may want to stick to the sound you are familiar with. If you have decided on a workstation, you may want to venture outside City Music to have a look at other brand names (Yamaha MOTIF, Roland Fantom).
If you need a (quote) "workstation with a reasonable depth of synth editing for beginners" (unquote), basically you can choose any workstation since they all do that.
If you can answer the above 4 questions, I think we can help you narrow (or broaden) your search.
In the end, it's criterion number 5 that will affect your decision - I call it the "X" factor. Or put it simply - personal preference. No matter what everybody says, one model/brand name just clicks with you and you'll pick that!