I've actually no idea if there is a priority security lane at T4 as I always use the TSA-Pre lane which is usually reasonably quick?
The new Delta One lounge is roughly half way inbetween the VS Clubhouse in the A gates area and the DL B gates SkyClub as it's not far from where you enter T4 after coming down the steps / escalator from security / check-in.
There's also a new(ish) DL SkyClub in the A gates area near gate A8 now which I've not tried yet as well as well as the old SkyClub lounge in the B gates area near gate B31.
The A gates area is (or at least was) getting renovated when I flew home in April so there was lots of hordings in place around several of the departure gates all with VS advertising on them so clearly VS are making the A gate area their permanent home in T4. I've not had a B gate departure with VS for many years now and even then historically it was generally just the MAN flight that arrived / departed from the B gates.
I really wouldn't bother the the B gates SkyClub as you will have to queue to get in that plus it's a trek to get to it. The only thing going for that lounge is the outdoor Skydeck area. I'd guess you will need to queue to get in the A gates SkyClub as well as queuing to get in lounges is now a thing with Delta
This page shows you the locations (zoom into T4 and then select level 4 to view the lounge locations and level 3 for the departure gates)