G'Day Tez
I currently use a nightforce scope on the CatKiller and if you can afford one you wouldnt regret it.
Other scopes I have used on varminting rifles are
Vortex Viper 3-9x40 Duplex (Lives on the camel rifle now). This is a good scope with great glass for the money. It was this scope that sold me on the Vortex brand. Had I bought the one below first I might not have been as enthusiastic
Vortex Viper 6.5-20x44AO Duplex Lives on the 17HMR. A good scope but not as good as the 3-9x40 of the same brand. I really havent had a chance to try it out much yet but for the price I couldnt argue with it.
Bushnell Elite 3200 4-12x40 AO (sits on the shelf gathering dust). At the time I was happy with this scope but now that I have used better ones I doubt I could go back to it. When my kids get there own centrefire they will get this scope.
Leupold VX-L 4.5-14x56 Duplex (Elmer Fudds scope on his .223). Bloody excellent and would be my pick in the scopes you are looking at in the >$1000 range. Its worth getting a price locally because sometimes with the dollar like it is you can get them cheap over here. this was the case for Elmer, a full $150 cheaper than buying OS. More often than not though TOZ is the cheapest for these (you can get the Alumina flip back protectors for them as well)
Redfield something or other, an old steel bodied scope that I recall throwing at the dog when it was digging up the lawn. It was on the old model70 had an adjustable objective and was obsolete and crap. Apparently it was a good scope in its day (circa 1979)
Simmons 3-9x40 duplex that was bundled with a rem sps I have since sold. The scope I gave to Elmer to put on his goat rifle and it still seems to work, essentially cheap but better than the redfield
On an overall preferance thing for long shots I like the AO if its all close in its a PITA. Magnifications, I have come to the conclusion that anything more than x15 isnt that usefull. I rarely use the NF wound out to x32 under the light as it loses so much brightness. Infact the only reason I can use it at this power is because we have shifted to HID lights. Weight isnt an issue for these sorts of scopes as I shoot from a vehicle or a stationary position. The CatKiller and Nightforce combo is heavy and not something that is a lot of fun to walk with.
Most important for me is a good consistent cheek weld to the stock and clear optics. the VX-L gives this with VX-III equivalent optics and low mounting. The scope for the 280AI will most likely be a VX-L 3-10x50.
Not sure if this helps or not Tez but there you go
Dr G