will this be better

[lost lemon]

so i have the amd a8 7650k cpu and a gtx 970 rn and saw a deal for a Dell Optiplex 7020 MT - i7-4790 for £40 i was wondering if it would be a good upgrade compared to my pc if i was to put the gpu in that with a different psu

[RONOTHAN##]

Yes, a 4790 will be a massive improvement over a Kavari APU. If it's only 40 gbp it would be well worth it. 

[Crunchy Dragon]

If your PSU will fit in the Dell case and be compatible with the Dell motherboard, that's not only a steal, but a really good upgrade.