5.8.6 is discontinued, IIRC it was an attempt to add Xorg 7.0 to plain 5.8.
Does that mean that there will not be a 5.8.6 stable version ?
1) Get VL 5.8 Soho Edition. It is a final release, surely you'll have a working x. Works great, it is well tested. It ships xorg 6.9. If for some reason you need a newer xorg, this one is not for you.
So here is my experience with SOHO edition :
I had already tested GOLD unsuccessfully a long time ago and thought that GOLD version was an ameliorated FINAL version ! So I finally found that the release date of Wednesday 12 September was for the year 2007 (and not 2006) !!

Anyway, I installed
5.8 SOHO Final :
During setup process, at the X.org server auto config step, it is asked to choose between ATI and FGLRX drivers. If I choose ATI, the X server auto config step restarts from the beginning !! So i have to choose fglrx. Using fglrx, I restart my computer and everything goes fine until the login step : I can see the TUI login screen for about half a second, then the screen becomes blank and the computer freezes totally : impossible to go back to TUI console (I tried Ctrl+Alt+Bckspace, Alt+F1, Alt+F8, Ctrl+Alt+F1...)
Then I Installed
5.8.6 SOHO RC2 :
Same problem at the Xorg config process. I then restarted my computer for first use : after TUI login screen, I've got a blank screen BUT i can go back to TUI console to manually configure my xorg.conf. Then Xorg starts with KDE !!

BUT : impossible to get a wifi network connection with vwifi

(unlike I did when I installed VL STD 5.9 RC2)
Using vwifi, i have to enter network SSID manually because nothing happens when I choose the automatic detection (strange because wifi-radar works when I load it manually).
Then i cannot connect to a WPA encrypted network.
With
5.9 STD RC2 :
Everything works fine and smooth.
But if I install KDE with slackware packages i suppose there are chances for KDE to be unstable ?
If everything works fine with 5.9rcX, my advise is waiting for it to become stable and go with it. I don't know if it's already stable enough to install it as a normal box.
If I can't get internet connection with 5.8.6 I think i'll do that...
Just a little remark : the text-mode installer is really fast and easy. Keep it like that !!