300 ppm sulfate is getting near the upper end of sulfate in brewing. I've heard of some brewers recommending 350 ppm, but I've found that 300 is good enough. In discussions with Colin Kaminski, he has indicated that he has pushed sulfate to 800 ppm and 'he' enjoyed it. But since he is a commercial brewer and his customers apparently did not enjoy that level, he uses a more modest level in his beers.
You do have to be aware that elevated level of sulfate can produce a sulfury aroma in beer. The 300 ppm level is well below that concern, but many brewers try to emulate a Burton level of sulfate that could be as high as 800 ppm depending on the location of the well. Fortunately, most Burton breweries had enough dilution of the deep sulfate-rich groundwater with less mineralized surficial groundwater that they probably didn't have to brew with sulfate levels that high.
Many commercial brewers brew with modest levels of sulfate. Unfortunately, they don't typically define what that level is. In comparison to the 600 to 800 ppm sulfate typical in many versions of Burton water, the 300 ppm level is quite moderate. For a hop-focused beer, I recommend that 100 ppm sulfate is the minimum I would use. The beer tends to be too bland and lacking crispness and hop expression if you go lower.
PS: the 300 ppm level is recommended by Randy Mosher.