I have run plenty of surface grinders with 3/4 Hp and they did just fine with the wheel diameter that fits the RPM..and the stock removal that dosent slow the RPM greatly/
3 or 4" (small) wheel does not give more power to the grind, when you get your Surface speed slow enough you begin honing, not grinding
surface speed is what makes grinding work and in the rough ballpark of 5000sfpm is what you need SFPM plus, up to around 6000-6500 with watching out for the specified RPM on the wheel label..
It does give more torque and therefore help prevent stalling though. You mentioned a 1½" wide wheel, that's pretty darn wide for ¾ HP. Could always compensate by using a harder wheel at the smaller diameter. Even so, it's a tricky game grinding very hard steel without the proper wheel and speed. And preferably flood coolant. Like Roger mentioned, it doesn't take a whole lot to cause all sorts of trouble. Probably the best approach all told is just to use the right wheel speed and have enough horsepower to do the job.