MDig,
I agree with quickdtoo on this one, a 3-9X40 for the .243 is ideal with maybe a max of a 4-12X40. I have a Weaver Classic 2.5-10X40 on mine an and it does the trick. I use it on everything from coyotes to prairie dogs to deer. I just was at Cabela's Sunday exchanging one of their PineRidge 4-12X40's(it would not change powers) on a Bushnell. I looked at the 3-9x40 Legend (very nice and 160 with free 20x50 spotting scope on the website), 3-9 Trophy(89.95) and a 4-12 Banner(99.95). Don't spend the extra on the 50 mm lens, just put it toward a better scope in a 40mm lens. You will also need to go to High Mount rings to use a 50 and thats a different accuracy issue.
I got the Trophy 3-9x40 and thought it was just a little better than the Banner. Now I have to decide which gun gets it, a .223 or the .270. If you will go the extra then look at the Burris Fullfield II in a 3-9x40 with the Ballitsic Plex reticle. If you like that type of recticle, the Trophy now has one called a TRW for 99.95 and would be the ideal all-round scope for around $100. I would have got it but Cabela's did not have it yet.
Good luck. I spent weeks researching scopes before I bought my Burris last fall. Let me know the price range and I can make some suggestions.
Mark