Welcome to the forums!! Have a http://www.uesp.net/w/images/images.new/c/c4/Fishystick.jpg.

Are you running the latest http://www.gamesas.com/index.php?/topic/1164539-relz-unofficial-oblivion-patch-320-unofficial-patch-supplementals/? I ask because Arthmoor did a lot of work to stop CTD's while running around outside. There are a couple of areas in particular that are prone to crashes. Also if you are running the latest UOP supplementals, you won't need the ThievesDen - Unofficial Patch - SSSB anymore and you actually have to remove that one or the area where the vendor shows up won't be accessible.
Also, when you upgraded to 4.1.8, did you follow the upgrade instructions in the readme? This is the downloaded version. There have been a number of changes to the ini file, so the upgrade instructions need to be followed exactly.
For Supreme Magicka, I suggest you turn off Oblivion XP's magicka regeneration if you're using SM's. That's what I do myself.
You also might consider installing Wrye Bash and creating a Bash patch. You don't have too many mods loaded, but a Bash patch will help ensure that all your mods coexist better. I'm not sure if you can run DR6 without a bash patch - it would be better to ask on the DR 6 thread about that.
Lastly, the only other thing I see that could be a problem is Francesco's increased spawns, which it appears you have loaded. I have seen a lot of instances where people have trouble when that feature is activated and you might consider removing it. Some of the spawns have some odd spell effects associated with them and I've read posts from people that say they start to experience crashes as they approach an area where one of these creatures is. There's actually a really detailed post http://www.gamesas.com/index.php?/topic/1140643-please-help-me-not-again-a-100-reproducable-ctd-with-a-fresh-install/ in which Skycaptain determined that it was a specific creature that was causing his crashes.
I think it's just coincidence that you started to experience crashes after upgrading to 4.1.8, as long as you upgraded properly. I have actually reduced the scan area in 4.1.6 and onwards, so you should get better performance and experience fewer crashes. Oblivion XP has an array that it uses to track all the creatures and NPC's in the area around your character. By reducing the scan area, that array is smaller.
It looks like you've used BOSS on your load order - if not, I strongly suggest you do.
If you're still having trouble after trying some of these things, let me know and we'll see if there's anything I can do.