BCoates,
With scopes you generally get what you pay for. If you're into F-Class for the long haul, then get a good scope first up if you can afford it, because you will definitely get one (or more) down the track. I've been shooting F-Open for over 10 years and have had Leupolds, a Weaver, a Sightron, and most recently a Nightforce Competition. The Leupold Vari-X IIIs (6-20X and 8-25X) have only 1/4" clicks, and have some minor focus/parallax issues. The Weaver T24 is poor optically. The Sightron SIII 10-50X is heavyish and optics could be better. I decided to get either a NF Competition 15-55X or the March equivalent. I asked for opinions on this forum from people who'd used both, and the NF was preferred by nearly all replies, which included some private messages. So I listened, bought a NF Comp, and have no regrets. It pretty much ticks all the boxes for my requirements. The optical clarity and brightness have made a real difference for reading faint mirage.
Regarding reticules, my advice is to decide how you will use it before selecting one, because there are three basic modes of aiming in F-Class, and each is suited to different reticules. If you intend to wind the windage knob and aim at the centre of the target, then most shooters prefer a dot type reticule, because it is easy to see when a dot is in the middle of a target ring. If you prefer not to wind, and hold off on the target rings, then a plain uncluttered cross-hair is often preferred. Or thirdly you can hold off using tick marks of a known interval on the horizontal cross-hair, and there are various reticules which provide that. Regardless of what your aiming mode is, I would recommend reticules with a full width horizontal cross-hair to help with controlling canting - most target frames are level, and its quicker to check for canting error through the scope than checking a bubble every shot. Another important consideration is the mils/MOA decision. For F-Class its a no brainer, go MOA. At tactical matches they may talk in mils, but in F-Class most of us only know MOA, and mils are like a foreign language.
Good luck with your purchasing decision.