I’m at the point where I now have 16 4 star charters chapped (highest 278) and another 7 or so that could be chapped or one cover away.
In five star land I have OML (3/3/1) at 300 and then the rest at 255…
BB 2/3/3
BW 0/4/2
SS 0/3/5
JG 3/0/3
BSS 3/2/1
Hulk 3/2/1
Is there a rule of thumb on when I should start leveling my five star guys?
Most aren’t useful till at least 10 covers (except oml)
with 16 4s champed I think you could take your oml up as high as you wanted. and your bolt can be leveled some, but not sure how much or how useful he’d be (mine is stuck at 1 cover). I would not pass 360 with my second 5* until I was ready to take a bigger plunge. leveling one increases difficulty a little but you have a more powerful oml to deal with it and will always have a good option in pvp and only need one decent boosted to make it a good week. and you have a good build going on him too. none of your others are close. if I were you I would take oml to 360 and see how things went. not sure on bolt. bolt is considered the top character in the game by many/most, but is less useful under-covered than oml is.
Your roster sounds very similar to mine. I have a 9 cover oml and 9 cover Thanos that I have leveled both to about 380 and haven’t noticed a big difference in my pvp mmr or pve scaling.
I can answer your question with another question…
When should you level your 5s?
When would you like to change pvp into ultra boring mode?
Seriously most non whale 5* players will tell you. You face lots of Oml/Phoenix teams and will be forced to use only your 5* your 4s will become a distant and nostalgic memory
this won’t be your experience with one at 360. I have one at 405, one at 360, one I’m leveling currently at 340, and that is not my experience. I have over 30 4* champs, but one 5* is safe. get him high enough and you might have to lean on him a lot. but I didn’t run my 405 oml when ice and peg were boosted and I’m only playing him about half the time this week with xpool and peg boosted.
Ahh you’re right. Of course I’m referring to MAXED 5s. Please accept my humble apologies for misreading. It is nearly midnight here and I have been working for 17 hours…had a lapse in concentration
So today…with OML at 300 (just got another red from a token poll so I can move him to 375) the highest node in pve goes to 321 at max level
If I move just OML to 360 will that node stay around 321 or go up much higher?
With 16 champed 4*, you’ll have a couple boosted in almost every event; at level 270, this means level 355 (more if it’s a featured character or essential). So you should be able to safely level the 5* to around that level or a little higher (370 or so) without impacting scaling/mmr. This is what I’ve read the others in this thread as saying, but they didn’t say it that way 
I wish I had this problem; my 5* are flat out not useful yet.