For your symptoms you ought to really consider an SSRI/Bupropion combo. Effexor may work very well for you though. Everyone reacts diff to all meds, with that one in particular though, most people either love it or hate it.
I have your exact symptoms and for me as well as many others on this board, remeron is pretty well known for making those things worse. I would sleep like a baby, but brain fog, lack of motivation, focus, everything else, etc etc, were all magnified much worse.
I also tried California Rocket Fuel in many different dosage combos. It was a nogo for me. Although I didn't try it in the highest doses of both. Say 375mg effexor with 45mg remeron. That may work for you as long as the extreme antihistamine reaction doesn't kick your *** too much. For me the more remeron I took, the more tired I got. If Remeron didn't have that Histamine antagonism it would be pretty damn great. Maybe there is something else with a similar profile.
I won't say much on how Effexor was for me on it's own, because I was one that didn't really like it. One thing in particular was extreme short term memory impairment, where normally without I was pretty sharp. I was seduced into it because the first few times I took it I felt very great, then after that it was pretty much all down hill. Though I will say if you're going to give it a go, definitely work up to the higher doses because they are better, especially with your symptoms. The withdrawal is definitely a pain, but if you add 150mg Bupropion XL while tapering off it makes all the difference in the world. If you're still having a hard time, a couple stretched out doses of prozac will go a long way because of it's long half life. And also either benzos here and there, or a mood stabilizer like Trilepal to take the edge off. I've been on and off many drugs, but Effexor was the only one that left me in an extreme hypervigilent state of mind when I stopped. Had I had something to chill me out at the time, it would have gone a long way. I'm possible Bipolar though so don't take that to heart. But yeah as you've said, it's pretty well known for having a horrible withdrawal.