I have to go to crimps at about 60# depending on which brand flouro I use. The Seaguar starts getting pretty beefy at that weight while the Yozuri seems to be a little more supple and will still take a knot OK... lots of lube helps.
In many cases you can stick to mono and save the $$. For example, I think using flouro for seabass is total waste as they have never shown me to be very leader shy..... there are a couple guys that tie for their own shops that don't believe in using anything but mono for rigs. But like you, for fluke and striper I am using 40# flouro, and the knots above work fine.