My original thoughts were that pedalling one of the newer 5s around the south downs probably wouldn’t be as fun/nice/pleasant as pedalling a machine that was lighter, more efficient at pedalling and better on tighter terrain. The 5 (and, to show I’m not making it up, my Heckler) are both great for blasting down and around steep, rocky, choppy (alpine/mountain) terrain but if I was riding wooded singletrack, moorland trails or smoother tracks without lots of big drops (<2ft) I’d get something with a bit more finesse. Such as the ST4, Commencal Super 4 (other half bike, upped the rebas to 120mm – now it is perfect for mile munching ups and technical downs).
If I lived in the Lakes or went to the alps regularly then maybe I’d contemplate a 5.
I have also demoed a Mythic/Banshee Spitfire and that was something of a revelation – it felt nimble in twisty terrain, climbed better than my Heckler and descended beautifully. It rewarded careful riding so much more than my Heckler, which acts a bit like a bull dozer, but also felt capable of more types of riding than my heckler. So far the best interpretation of a UK full sus mountain bike I have ridden (i.e. a bike suited to most aspects of UK trail riding rather than a leftover from an Americans Freegnarlridecore marketing exercise). It is what I imagine the ST4 would (should have been, or is there an ST5 in the works?) be like if you were allowed a longer fork.
At the end of the day get the bike you want, it’s you it has to make happy, not anyone else.