Super R-Type was the 4th game I acquired for my SNES after receiving the system in September of '91. I spent a good deal of time playing the game, but I don't remember ever passing farther than the 3rd level without using some sort of cheat code. I'd try again in my old age, but there just aren't enough hours in the day to devote to tedious video games.
And there was quite a bit of slowdown in this game, but the epic soundtrack did a lot to distract from that issue. Back in the early 90's I had my SNES hooked up to a pretty decent stereo system and used to record the game audio onto cassette tapes to play in the car...much to my parents' chagrin.