I'm not suggesting you try what I report. Just FYI.
I've tried each of the following full doses individually: 100 mg Viagra / sildenafil, 20 mg Cialis / tadalafil, 20 mg Levitra / vardenafil and 200 mg Stendra / no generic. I've tried combinations up to one-half of each of the four above - which is like a double dose of any single med. These meds are all called PDE5 Inhibitors and pretty much work the same way. But the latter three meds have less 'Viagra burn' i.e. the 'sunburn' from Viagra.
I've done each individual med or combo at least 5 times with a partner, as 5 tries is recommended to get a baseline. Many variables influence male response and it's difficult to tease out what, if anything, works better absent a lot of tries. If I had to choose two meds to single- or double-dose I'd use 20 mg Cialis / tadalafil & 20 mg Levitra / vardenafil. While my ED improved on PDE5Is, I was not satisfied.
Finally I discovered what helped me the most. I stopped two meds I've taken for 20 years to treat BPH (a very big prostate). Over time, tamsulosin interfered with erection and finasteride became the off switch for ejaculation. BTW 5 mg Cialis / tadalafil is approved to reduce BPH symptoms so I take that daily in place of tamsulosin & finasteride.
What is my latest experiment? Muse - a urethral suppository. There is absolutely no discomfort using the applicator to dispense the tiny pellet into the bad boy. Result? After 10 minutes I have three hours of hard fun - just like I was young. No matter what, I stop having fun at 3 hours to make sure I deflate well before 4 hours - when I'd have to go to the Emergency Room for Priapism. (Did you see my screen name?) I still take the PDE5 Inhibitor blends with the Muse.
I've told my urologist what I have done. He said: 1. I was mega-dosing on PDE5Is and increasing risk of side-effects. 2. Don't expect combos to help because they all work by the same PDE5I chemistry. 3. Mixed PDE5I use is off-label, i.e. not backed up by any science, hence not recommended. And yes, he was quietly pissed. I told him I took my blood pressure and it never dropped dangerously low. That would be the most likely way I would hurt myself. Still, he's only writing Rx for Muse and Cialis since my disclosure.