You already know my feelings on ~300ppm sulfate levels so I won't reiterate them. One thing is true though: You'll never know what 300ppm sulfate levels are like unless you try them (at least once)
. In other words, how will YOU ever know if YOU like those levels unless YOU try them in a beer? YOU won't, so you have to try it. Definitely try them and decide for yourself.
As for trying them out for a party beer, that's up to you. High sulfate levels are noticeable and not always welcome. If you're dealing with folks who are regularly drinking the most bitter IPAs found these days then they probably will be accustomed to high sulfate levels in their beer and won't notice/mind too much. Aside from those heavily-bittered IPA drinkers, most folks will notice a character or sensation in the beer (for better or worse). 200ppm should be fairly noticeable too, but not quite as "gripping" as 300. If you're brewing a bitter hoppy beer then give it shot, or aim a bit lower to play it more subtly.
What beer are you planning to brew for St Patrick's Day anyway?
As far as conditioning beers with high sulfate levels, I've never experienced or heard of a difference. It should condition as quickly as any other beer in my book.