Wick,
I have had a Sebenza since 1993. I love it. It it just as smooth as when I first got it, and the handles have a lot of character. I have 10 years of everyday experiences with it. It is a solid knife, and one that I think will always remain a classic. Enough said.
As far as the mayo goes, I'll try and decribe it best I can. Light, SMOOTH, slim, perfect size in my average hands. I had on lightweight North Face nylon shorts, which tend to weigh down when I carry a knife in the pocket. ( my EDC has been a Strider SnG for the last couple of months) I stuck the Mayo in there, and I could hardly tell it was there. That was nice. But in hand, with the blade open, it still felt very solid. The lock was very positive, and engaged with a crisp feel to it. I remember thinking that the blade had a higher polish to it than I expected. It looked good paired with the satin look of the titanium. The only thing I could think of at the moment was I need to order another one. I'll put the second one in my safe and keep it nice. I never thought I would have a Buck safe queen.
Now, to answer your question, is it a Sebenza slayer? I'd have to carry and use the Mayo for a time to make that decision. See how it wears, etc. From the little time I spent with it, I can tell you this. If I had $350 dollars and had to spend it on a knife. I'd beg, borrow, or steal another $30, call Larry Oden, and order two of the Mayo's before I bought one Sebenza.
That is just my 2 cents. I am by no stretch of the imagination a knife reviewer. I have never held a Mayo custom, but I am his list for one, along with waiting on Knifeart to get my TnT tactical in. The Buck knife has beefed up my anticipation to another level. There will be some guys who will be able to compare a custom to the Buck version, and I look forward to reading what they have to say. Hope I helped a little.
DB