Noticed while walking around Asda they have 4 litres of castrol gtx 10/40 on offer at £13. Semi synthetic

My 120 multijet 2.3 2007 manual states use 5/40.

Question is would the gtx 10/40 be ok to use, as that would make a mega cheap diy oil change?

realise I would require 2 lots, the acea is B4 compliant

I put that in my 2.8jtd and that is very cheap i am off there in the morning to buy 3 (for two oil changes)