Yeah, I wouldn't upgrade to the XT without a PSU upgrade personally. 650w would be cutting it fine, as others have said.
The cheapest 9070 non-XT on OcUK at the moment is £489. Adding RAM will most definitely go over the £600 I think.
The cheapest 9070 non-XT on OcUK at the moment is £489. Adding RAM will most definitely go over the £600 I think.