If you can afford the inflated price of DDR5, then go for it. I am on the pessimistic side on this as there are so many big players (Google, Oracle and even the US/PRC government are participated in the AI arms race), even OpenAI go bust due to running out of funds, others will continue the game and my guess is things aren't improving significantly before 2030, if you planned to upgrade by 2028, the chance is waiting isn't doing you much favour, to me the decision is probably either wait for 5+ years, or upgrade now, as for GPU, 5070Ti isn't providing good value for the current price and is not outperforming 9070XT outside the DLSS/RT perks, if you don't need top end performance (which u should go for 5080/5090 where AMD do not have equivalents) or saving money opting for 9070XT over the inflated 5070Ti today, just my 2 pennies....