I have traveled with a bag 72 x 50 x 31 cm about 5 times, and VA have questioned it several times but never measured it, and they have let it fly as normal luggage. I have to travel with it for work so I didn't have a choice.
I'm not sure what the VA linear size limit is, but I believe as long as it doesn't exceed 23kg it can fly for free as oversize, it just has to be tagged as such. One issue with big bags is that it can be difficult to keep them under the 23kg limit.
The Delta limit is 157cm, your bag is too big. I don't have experience in how strict Delta is on linear dimensions, but they are very strict on weight. I'm also not sure if they will let it fly or not if they decide it is oversize.