There are two or three logical approaches to the OP question.
Firstly as the mod says, what's the worse that can happen if you take 2 x 100mg? Going through the literature, not a lot (unless you have a severe condition that suggests you shouldn't take it anyway).
Secondly, the tadalafil option, which is a variation of the first. Tadalafil works over a longer period, even a couple of days, so one option (tried) is a (maybe low dose) tadalafil a day before and a sildenafil 'booster' from half an hour to a couple of hours before the event. (timing relates to your general metabolism and also if you have had anything to eat which acts as a delaying mechanism).
A third option is one that has been discussed on other threads and you can look it up. It's based on two facts: a) sildenafil and all the other PDE5i drugs work by enhancing the nitric oxide dilation of your cock. b) if your internal nitric oxide pathway is a bit fucked up sildenafil won't have much effect.
Some crazy medical researchers noticed that the amino-acid l-arginine enters the nitric oxide pathway long before the point where sildenafil connects to that pathway. Nitric oxide is a vasodilator, but it has to be already present for sildenafil to work. The remedy, tried and tested by several UKP members, is to take a decent quantity of l-arginine for a few days before taking your viagra. In fact many have found the arginine works even without the need for viagra. It's all to do with whether your nitric oxide pathway is fucked up in the first place. If it isn't, l-arginine probably won't alter things that much, but there's a big loss of nitric oxide with aging and also with high blood pressure which is also more common as people get older. You get a bag of l-arginine (easier and cheaper than capsules), add two scoops to a small glass of water and dissolve it, maybe add a squirt of lemon juice to improve the flavour, and gulp it down.
