Tried one when I was a teenager and it made me quite sleepy and out of it, maybe took too much. Definitely worth a try. I do have some benzos but just careful not to use them too much, they are perfect really but I want to keep my tolerance down and keep them for when I most need them.
I remember you PA from when I used to come on bluelight more often a few years ago. Hope you are well. I think I saw from searching for mirtazapine in the search engine that it seemed to agree with you. Was that on the 30mg dose?
Yeah Promethazine is pretty damn sedating even for me. When i was taking Histantil (the brand name for Promethazine here in Canada) for allergies and nausea/vomiting i certainly wouldn't drive on 50mg's of Promethazine that's for sure. However i found Hydroxyzine to be much less sedating then Promethazine or Diphenhydramine which is most likely because it has very little Anti-Cholinergic effects. It's probably the most used and effective Anti-Histamine for anxiety as it has effects other Anti-Histamines don't such as 5-HT2a receptor Antagonism. Other anti-histamines that don't act as Serotonin Antagonists don't work nearly as well as Hydroxyzine for anxiety so most likely this mechanism of action is responsible for it's Anti-Anxiety effects.
Oh you remember me? Now i feel special

Have you tried any Tricyclic Anti-Depressants such as Doxepin, Amitriptyline or Trimipramine? They do help some peoples anxiety and i have taken Amitriptyline and Trimipramine for Depression. Despite Amitriptyline basically being a SNRI with strong Anti-Cholinergic effects it caused absolutely no sexual dysfunction in me even at the max outpatient dose of 150mg's a day. Trimipramine also did not cause any sexual dysfunction and it may work better on anxiety because of the fact that it also has some Atypical Anti-psychotic effects. I would definitely say a TCA would be worth a shot if you haven't tried one already.
You also mentioned Quetiapine. I take this for Bipolar Disorder when the Lamictal doesn't control the mania granted at doses of 300-500mgs' which is alot more then you would use for anxiety or insomnia. For anxiety you wouldn't need anymore then 100mg's at which dose it does not act as a Anti-Psychotic at all really and is mostly a Anti-Histamine and a α1-adrenergic and α2-adrenergic receptor antagonist. Some people have luck with this in treating anxiety but i don't think it should be a 1st or even second line treatment due to it's potential side effects such as Type 2 Diabetes. I don't know if it helps my anxiety at all as the Clonazepam generally keeps that in check.