The brew temperature and the boiler temperature are 2 different things, and the reason for the difference is where the temperature is measured.
It is not very easy to measure the brew water temperature on a Silvia, but it is very easy to measure the temperature at the top of the boiler.
Depending on the calibration of your setup, the optimal brew temperature should be when the boiler temp is in the range of 105-109 degC.....taste is the ultimate guide.
If the brew seems bitter, try brewing at lower temp, if its sour try brewing at higher temp.
Not quite sure what you mean by not as intense as what you are used to. Silvia can produce exceptional results with some practice and consistency. Bean type and freshness, grind quality and grinding just before you brew all affect the outcome significantly.
Yes the baskets are relatively small, dont use the single it is also a poor shape as well as being too small, and almost everybody who tries it reports poor results with it.
The double is capable of great shots, and can be updosed a bit by tapping the pf on the bench to settle the grinds into the basket before levelling and tamping.
If you are concerned about caffeine intake using the double, then cut the shot short, it will still be intense, just less caffeine.
Hope this helps some.