Two oppositions ago I had a great time observing Mars using an Orion 100ED. All the mayor albedo features as well as the polar caps and, when present, clouds/dust are clearly visible with small telescopes and plenty of details with a 100mm. Olympus Mons has remained elusive with the 100mm. If my recollection is accurate, the best I have done is observing the clouds that sometimes form on top of the volcanoes using a 6” refractor. Filters help a lot with that as they are usually low contrast. Keep in mind that the duration of the Martian day is almost exactly that if a day on earth. So if one observes at the same time each evening one gets to see the same side of Mars.
Really looking forward to the next opposition. The last one was a bust.