It will be used only on Texas Whitetail. I love shooting the 243 and I will be reloading.
Based on that, I have to say get the 260. Load it with 100 grain Nosler Partitions, if you want, and you'll have a 3300 fps deer load that feels like that .243 that you like to shoot.
I've used bullets from 90 grains to 160 grains in my 260, and the gun liked them all, except for the 140 grain Nosler Partitions. At longer ranges, velocity fell off too far for good expansion. Uneven expansion then caused the bullets to tumble, spit out their rear cores, and produce relatively shallow penetration. My favorite all-around bullet for the 260 is the 125 grain Nosler Partition, followed by the 129 grain Hornady. These give the best balance for the cartridge size, good sectional density, and plenty of velocity. If you change your mind and go after bigger game with your 260, you can always load it with 140 grain Speers, either Grand Slam or Hot-Cor. The 160 grain Hornady also worked well for me, but I had to seat it pretty deep in the case to clear the rifling in my T/C Encore. If I was hunting big animals in timber with the 260, I'd use the 160 grain Hornady.
For varmints, I favor the 90 grain Speer TNT HP. You have to go to their web site to get the loading info for that bullet, though. Other outfits make lighter bullets, if you're into setting speed records. The Speer will break 3300 fps from my 24" barrel without using a max load, so my brass lasts very well.