What velocity are the F/TR shooters getting with 90's in a 223 and with what barrel length?
At the high end with a 30" barrel, Lapua brass, and sufficient freebore to seat the 90 VLDs properly in the neck, there is a very nice node at ~2850 fps with H4895. Varget loads will likely tune in at ~25 fps slower. Brass life with such a load is typically
poor...MAYBE 4-5 firings before the primer pockets let go. Some will be done after 2-3 firings. Nonetheless, such a load can shoot very, very well, and some are willing to accept the poor brass life.
For those that tire of replacing Lapua brass that often, there is also a very nice node with 90 VLDs at ~2775 fps using H4895 with a 30" barrel, maybe 2750 fps or so with Varget. One gives up just a tick of resistance to wind deflection with the slower loads, but will be compensated by much better brass life.
Whether one chooses a bullets such as the SMK 90s, 85.5 Hybrids, 88 ELDMs, 90 VLDs, or 95 SMKs, using a 28-32" barrel length is common in F-TR. The use of various powders such as H4895, Varget, N140, N135, N150, and probably a few others means subtle differences in tune windows, so the chosen bullet/powder/case volume/freebore can make a significant difference in where each load will tune in. There are also subtle difference in BC between the above-mentioned bullets. However, performance with any of the ~85-95 gr .224" bullets should be a noticeable improvement in terms of wind deflection as compared with .224" bullets in the ~80 gr weight class.
For the OP - if a 26" [finish length] barrel is what you're going have, go with it. It will certainly work, although you may find loads with heavies tuning in at velocities well below what can be achieved at comparable pressure from a longer barrel. I'd expect something in the 2700-ish fps velocity range would be a realistic expectation for a moderate load with the 85.5s and a 26" barrel. You might be able to juice that velocity up a little bit, but will potentially pay the price in terms of shorter brass life. At ~2700 fps muzzle velocity, the 85.5 should remain supersonic out to 1000 yd. Predicted wind deflection at 1000 yd will be higher because of the lesser velocity, but you can think of that as useful for honing your wind-reading skills. You will also be learning about how your bullet of choice behaves, and what it wants in terms of load development. While you are enjoying shooting out the 26" barrel, you can put in an order with a barrel manufacturer for a longer blank, or regularly check online vendors, so that you have another blank in hand when the current barrel nears the end of its useful life.
As has been noted by several others above, you need to inform the gunsmith exactly what you expect to achieve with the setup, and the gunsmith will determine the best way to get there. Good dialog and a friendly relationship between customer and gunsmith is a recipe for success.