I've been using a 7x57 for the past 25 years. Mainly for roe (30+/yr) and for a few red mostly at the rut and also for foxes. It's never let me down on any of them. I was tempted to buy a .243 barrel last year and was going to sell the 7x5 one. Alas, the .243 still sits in the cupboard and first choice is the 7x57. Love the 123gn bullets that RWS did, but also the 156gn Norma's. Both are good for anything, the 123's are my preferred choice for foxes, but the Norma's get the job done on deer with little to no mess on the roe.
Never shot a 6.5 so can't compare