Realistically it is not practical to sustain 30+ mph on an ebike without a proper suspension system. Your interest in high power stuff does not go with your stated desires for the bike (Wal-mart grocery run).

This bike fits your grocery run perfectly: https://www.radpowerbikes.com/produc...=5032655749151

Regarding speed - in most places there are laws on the books prohibiting riding ebikes on sidewalks, and most bike trails have a 15mph speed limit - enforcement is usually non-existent......

My 36V 500W front hub ($150- from Amazon) converted 1992 Trek 950 with me on it (400-450 lbs GVW) will go 26-29mph (depending on battery charge level) with no pedalling, for more than 10 miles (flat out) on a 468Wh (13Ah) battery ($300- from Amazon). Going a bit less than flat out (say 20 mph) and adding a little pedalling will get it past 20 miles easily.

A healthy non-professional cyclist in anaerobic sprint mode (a couple minutes at most) will put out 500W to 1000W. In aerobic mode 200-350W range.

Also note that standard bike tires are not designed for 30+ mph, a blowout at speed will result in a hospital stay if you are lucky. Make sure you get tires rated for the speed and weight you are carry. My 950 has Schwalbe Big Ben 50-559 tires.

On heavy e-bikes, rear spoke failure is common due to the lack of compliance, the shock loads the spokes are amplified by higher speeds. Larger tires mitigate this somewhat, suspension more so.