You'll lose a lot more speed with suspension than a small drop n PSI/slightly wider tire.
I don't think anyone here advised you to get a suspension fork, but hey, it's your bike...
I recommended a suspension fork. I have one on my 7300 Trek. It's not a race bike, but it's fast. The only time I can see it slowing me down if at all is now and then when I stand up and start seriously hammering then it does bounce a bit. I don't hammer often, and when I do. Not long. I have it set as stiff as possible so it actually feels almost rigid. But when I hit a major bump, it gives. I find its handy especially when you don't see a bump coming up.