I got into foiling last summer having bought a Fanatic Flow 1500 and a Fanatic Stingray 140. I spent most of my sessions over the summer in lighter winds (12-15 knots) with my Foil Glide2 7m. I've had a few sessions recently where it's been blowing a lot more (20+ knots) and I've found myself struggling to keep the foil in the water. I also feel I'll soon be ready for a wing with a little less surface area that'll get me more speed.

In terms of next steps from a gear purchase perspective where is the next logical progression? Should I simply be looking to buy an 1000 front wing only to use on my existing set up (~$800)? How much of a difference can I expect between the 1000 and 1500? They also have a 900 available but I was reading somewhere on this forum that this is an old shape and slower for some reason. I've also seen a guy out on the bay with an IQ Foil rig (Simon) and the guy is FAST but I think that kit is fairly expensive (~$4k+).

Thoughts on options?

For reference I just enjoy blasting around the Port Phillip bay year round and am not looking to get into any kind of racing.

Sails:
Severne Blade 4.7m, 5.3m
Severne Gator 6m
Severne Foil Glide 2, 6m, 7m

I have the exact same set-up and also have the 1000 frontwing. Once your technique gets better, the 1000 fronwing is all you need. This thing is fast!! But more forgiving then other real race 1000cm2 wings. Buy it, you will not regret it.
I am waiting for the carbon Fantic Flow mast and fuselage but the introduction has been delayed.

I started out on a Stringray 125 with the Flow 1250. I'm around 78kg and would probably be considered intermediate. On occasion I'll plane out of a gybe still struggling with them. Recently I purchased the 900 front wing, not because I particularly wanted a new wing, but because it was a bargain...less than $300 delivered from QLD. I've had about 3 sessions on it so far, the windiest gusting to 25. The first thing I noticed was the speed. It's a fair bit quicker than the 1250. I've yet to really test the bottom end but I'm thinking I'll be spending most of my time on the 900, only changing to the 1250 when below 14 knots. I reckon the 1000 would pair nicely with your 1500. Should give you a good wind range.

On an AFS with F1080 and F770 cm2 wings, the F770 is a lot easier to control in high winds +20 knots, when a gust hits can use just front foot pressure to keep foil in the water, while the F1080 needs more like sheeting out and/or heading up wind and if you do not do that fast enough you go flying. So a 1000 cm2 wing may be too much for high winds, just depends how much lift it provides. The F770 is fairly high aspect.

Flow 1000 is perfect 1 foil solution for those conditions. When it gets windy you just need to change down sail sizes a bit sooner if you are struggling to keep everything under control. If you are just foiling I'd definitely slim down your sail quiver, I'd jump straight from the 7.0 to the 4.7 or 5.3, and add some smaller sails to your quiver.

I change down fairly early, but I'd say approximate wind ranges for me at 80kg with the flow1000 is around:
6.0m - <10kts - 16kts
4.8m - 12kts to 18kts
4.0m - 14kts to 20kts+
3.3m - 18kts to 25kts+

I'm not a huge fan of the 6m foilglide, just because I'd much rather use a lightweight wavesail, I'm sure its good for much more than 16kts of wind, and if I had a wider board like yours, the 7m would be the one I'd keep. I'm considering dropping it for a 5.6m Freek or something similar. But I'm pretty biased towards smaller sails, on the opposite end of the spectrum, the IQfoil guys hang onto a 9m, from 6kts - 25kts.

It's am also interesting to purchase the Fanatic flow 1000 but I hear it make an annoying whistling noise when you foil is that true ??? Thanks

As you asked elsewhere, it's not the front foil, it's the stab.