I think the Discmania FD and FD2 is probably one of the best FW combos out there! The feel of both discs is very similar, they're the same speed, and they can cover a TON of shots between the two of them in different weights/plastics.
The FD in a light or mid weight in S-Line would be your super glidey turnover FW. A color glow, S-line or C-Line in mid to max weight would be your long glidey dead straight FW.
Then a mid weight FD2 in either S-line or Color glow for your stable to slightly O/S FW. Then a max weight C-line or Color Glow for your O/S FW.
The FD2 (depending on your power) is more of a hyzer disc. It either goes straight for a bit, then starts gently sweeping left about 2/3 of the way through it's flight. Or, if you absolutely crush and throw 450-500+ on avg, it will fly more like the Instinct. With that straight flight with a solid hook up left at the end. I don't have that type of skill/power yet, so for me (I throw around 320-340 on avg drives) it is my stable to O/S FW. If I have a shot I CAN'T afford to go right with, yet don't want a ton of fade either, I reach for my FD2. It has a little less glide then most FWs, so it has more control. You have to THOW it to get there. It's not going to glide there. It's almost impossible for me to turn it over, yet, it doesn't have a huge fade or hyzer either. But, if you want to throw it on a push hyzer where it fades the whole way, you can easily do that as well. I've even seen a buddy of mine throw his hard on a slight anny and get it to go right a little, then gently come out and fade left near the end. If I throw it well and flat, it goes about 2/3's of the flight dead straight, then starts a gentle sweeping hyzer at the end. And can get some good skip if thrown low. And it's hands down the best FH disc ever! Eagle used to use them for almost all FH shots! Still uses them sometimes and holed out at the Idlewood with it on a SICK anny FH shot either last year or this year!
Both discs feel almost the same to me, and can cover most FW shots as a pair, and both are the same speed. They are also both super versatile. You can FH or BH both with amazing results and get a LOT of different lines out them.
I'd also add that the new Instinct is also a KILLER FW disc that is right in between those two and is somewhat similar in feel, and the same speed. The FD and FD2 have a more flat or semi rounded wing shape, while the Instinct has that more scalloped out shape. But it's not a huge scallop. And the rim width and overall disc shape feels along the lines of the FD/FD2. Not the same, but not a whole lot different. And it is an incredible FW disc! It's a point and shoot bomber. It has really good stability against hard rips, and then hooks up left at the last second with a forward penetrating fade. If you throw around 300-400', it's dead straight for 90% of it's flight then with a 10-20' forward pushing fade right at the end. It's such a cool flight path! And if you throw 450-500+ on avg, you might get a small turn right or you could hyzer flip it up to straight and it just GOES! But once again, it always comes back at the end. So reliable! It's turned into one of my favorite most reliable FW discs I've ever owned. I throw it all the time now. It's taken over as my favorite FW from my beloved FD's. And sneaky long as well. Id say it's more like a glide 5.5
And if you wanted to book end both, you'd go with either the FD3 or a FireBird for the super O/S FW disc slot. With the FD, FD2/or Instinct and FD3/FB, in different weights and plastics, you'd be able to cover EVERY shot for a FW disc.
But... the only problem with my suggestion is that Discmania is no longer making the FD or FD2 for the time being. You'd have to wait till probably next summer or longer to be able to get both.
But if you can find any of those discs, or get them next year (if they make them) that's my suggestion for the best pairing of FW discs that feel pretty similar, have the same speed and complement each other VERY well! Haven't found anything else yet that's as good as those two! Good luck