Firstly, you're asking between latex and oil, satin impervo, unless you mean the latex impervo. All waterborne and Genex products are difficult to brush, as they are thicker and set more quickly. However, I have found that they are more forgiving than traditional latex enamels. What I mean is better leveling and forgiveness if you stray back into an area that has begun to set. Alkyd satin impervo is easier, but it has it's little tickles as well. I used satin impervo exclusively for a decade or more, and saw many experienced SI newbies come through struggle to achieve SI's hallmark spray like finish with a brush. In the old days, before Uncle Sham stripped the paint industry, I would put that stuff on and you would have lost your shirt if you had bet that it was sprayed. My advice to you would be to not change horses mid-stream if the rooms are contiguous. Stick with uniformity, use some Floetrol and maybe a few drops of water, and loosen the stuff up enough for more ease in brushing. Start out slowly with the additives, a bit at a time until it works for you. It's too wordy to offer brushwork tips in this format, but if you're interested you can contact me through my blog below, there's a contact form there. Good Luck.