I've got the VX-6 3-18x50 and 4-24x52's on six different rifles. All are mounted with EGW HD rails but one which is on a Near 20 MOA rail and all are mounted with low or med/low rings.
The difference in weight between the 44, 50, 52mm ob is less than one bullet. I have three of the 4.5-14x50 tacticals mounted similarly.
To me, the larger diameter's added light gathering capability makes it more than worthwhile for the negligible weight difference.
I haven't owned any of the VX-5's but have looked through several and I very much liked what I saw.
Don't think you'll be making a mistake with any of them or even with the VX-3i's which are well worth a look too.
The only advantage to the MK4's is that they are really built to take a whole lot of abuse.