Hi Simsy, I love the El Salvadors as an so but have done some blends recently using them as the base. I roasted them separately and then post-roast blended them after resting about 7 days.
Using ES as base of 60% I added PNG Sigri 20% and Ethiopian Dima 15%, it produced a lovely fruity/choc espresso and cut through milk to produce a lovely flat white/latte.
Ive found roasting beans separately, you are able to adjust the percentages in blend to tweak taste I am seeking.
Its all a great learning curve................