Among the potential merits of fixed power optics include lower cost and lighter weight as compared to adjustable magnification scopes. However, there are also a couple issues associated with the use of fixed power scopes in competitive shooting such as F-Class. First, if the chosen [fixed] mag is too high, it can increase the risk of crossfire for some shooters due to limited field of view. Second, the magnification cannot be adjusted lower with a fixed power optic if the mirage gets really heavy. There are ways to deal with both the increased risk of crossfire and sensitivity to mirage, but both are considerations in terms of scope choice.
Personally, I wouldn't choose a fixed-power optic over about 36X for a couple reasons. Although I own a couple fixed 36X IOR-Valdada BR scopes, I have looked through other fixed-power scopes in the 40X to 45X range and the field of view is just a bit too small to easily see the target number boards at the ranges I shoot most often. I am one of those that WILL crossfire if I can't see a significant portion of the target number board. I find magnification of around 28X to 30X is more than sufficient for my eyes to hold halfway between scoring rings, even at 1000 yd. I can't reliably shoot any more precisely than that at 1000 yd, so greater magnification isn't a big selling point for me. In addition, the higher the magnification, the greater the perceived effect/distortion will typically be when the mirage comes up. I find dropping down to around 30X will usually minimize that effect to a manageable level. Alternatively, inserts are available for some scope designs that reduce the front aperture size and can help tame bad mirage, albeit with some reduction of light passing through the scope.
The bottom line is that what seems optimal to my eyes may be markedly different than what your eyes need. Looking through a potential scope purchase is the best possible way to let your own eyes judge any merits or liabilities the scope may have. You stated that you already own both scope choices, so perhaps you could list the pros and cons of each scope for us, and in doing so, it might help you make a decision.