You can't buy a 5070 Ti for £700, or even close at this moment in time. Currently OCUK have the cheapest 5070 TI available for £890 (
Link). Any game that supports DLSS 2/3 or XeSS can be used with FSR4 with a simple mod (
Link), same as it's always been for upscaling methods not officially supported. The cost of running a GPU is insignificant, there is around 10w difference in power consumption if you compare like for like models when running at full power. So even if you used both cards at max power for 20 hours a week (Which i don't have time for), that's a total of 10KWh over a year. 25p a unit, works out at a huge £2.50 for the year. When both cards are locked to 60fps the AMD is actually significantly more efficient, 80w compared to 110w (
Link). Again though i wouldn't base my purchase on power usage, I'm not sure why people bring power up when it's such an insignificant amount in the whole scheme of things.