I took recently the ACT test, which is simmilar to the SAT. Comparing the two tests in the english section, the ACT requires you to be more fast. Also, the vocabulary is easier than SAT, which has some awkward words nobody uses, like 'inebriation' and 'sycophant'. In the reading and writing sections they are equivalent.
Regarding my experience, I had problems during the test with time. Sometimes the tests are easy, but the pressure can lead you to a mistake. It's also very common to present some tricks, like a wrong use of commas in a sentence or wrong collocations. The reading test is very straightforward: all you need is to focus in some details they ask. And finally, in the writing section you have to be very fast to organize your examples to support your introduction.
I know SAT will change this year, if I'm not mistaken. They'll try to make the test more simmilar to ACT model, what I find good.