At F/5.6 color and FC is a problem like with all fast Achros.
Field curvature is an identical problem for APOs... No difference there unless the scope is corrected for field curvature, quite rare.
I'd keep them both or sell the ST-90 and replace it with an ST-80 with a 2 inch focuser. I have an ST-80 with a 2 inch focuser for the widest possible views plus an AT-80 LE which is an 80mm F/6 FPL-53 doublet which provides up to 5.5 degrees with very good color correction, slightly wider than is possible with the ST-90 with a 2 inch focuser.
And then there's more. If you really like ultra wide field sweeping and dislike field curvature, one the TeleVue Modified Petzvals would do the trick. The older ones have some false color, the newest, none. The NP-101 has a 540mm focal length, only 40mm longer than the ST-90 but a flat field and excellent color correction. These will do 4.9 degrees with a 41mm Panoptic, 4.45 degrees with a 31mm Nagler.