Different results from taking Viagra

I an 64 years old and in good health, taking no Rxs except for ED's. I started taking Viagra from the first time it was available on the advice of my Urologist.

What I don't understand is why I can have radically different results from taking the same dose under simular conditions.

The first time I took it, I violated most of the rules. I was in a bar feeling sorry for myself, got picked up by a lady, had several more drinks than I usually have, and smoked some of her cigarets. I had a fantastic erection that lasted through several ejactulations. However, I have never had that good of an erection since. I usually start out with a good erection, but if I spend too much time in foreplay, I am likely to lose that erection and sometimes I can get it back and at other times, I can't.

I have heard from a radio talk show, that I shouldn't eat a large meal with a large fat content ( for instance, ribeye steak with baked potatoe with lots of butter and sour cream) before using Viagra, as it is not as absorbed as well.

#1 Was that just a radio talk host blowing smoke or is there some truth to this?

#2 I am going on a 4 day cruise and I have been told by my new partner to expect lots of sexually activity as she gets like a tiger on a cruise. Can I use more than 100 mg of Viagra in a 24 hour period. Can I alternate with Cialis, as I also have a prescription of it? 

Are ther any other situation that would prevent either Rx from working as well as it should.

Thanks