I've experienced what you're talking about in group play, we had a rend barbarion (running pain enhancer) + I was playing HOTA with pain enhancer in a 67 Grift (3man) and it was impossible, it just lagged for eternity, but in solo play I've not been having any issues. Both Rend and BK/Wastes seem to be able to go above 70, but perhaps your lag issue is also the reason more of the top players are moving away from Rend.
I've not tried going above 60 in solo play as I pretty much always play in groups now, but when I was soloing I didn't experience big lag issues, only really happens in the 65+ group rifts, especially that one 67 we did where it was completely unplayable.
Have you tried IK 6 + 2 Wastes Rend build? I know BK/Wastes is starting to dominate the top of the leaderboards but I have tried all 3 of the popular specs and by far the easiest to beat a 60 for me was the rend spec, the damage seems much much higher and is doable without a great rift.
I didn't have any lucky pylons or great mob density and 60 was fairly easy, I was around Para 570 at the time. I'm not entirely sure how people are even reaching 70 with the BK build as it seems lacking in damage compared to the others, unless you're relying on a godly rift to fully exploit tornados.
Specific advice, your gems are really low level and you don't have a Hellfire neck, level your gems and make Hellfire necks until you get a good one.
I've experienced what you're talking about in group play, we had a rend barbarion (running pain enhancer) + I was playing HOTA with pain enhancer in a 67 Grift (3man) and it was impossible, it just lagged for eternity, but in solo play I've not been having any issues. Both Rend and BK/Wastes seem to be able to go above 70, but perhaps your lag issue is also the reason more of the top players are moving away from Rend.
I've not tried going above 60 in solo play as I pretty much always play in groups now, but when I was soloing I didn't experience big lag issues, only really happens in the 65+ group rifts, especially that one 67 we did where it was completely unplayable.
Have you tried IK 6 + 2 Wastes Rend build? I know BK/Wastes is starting to dominate the top of the leaderboards but I have tried all 3 of the popular specs and by far the easiest to beat a 60 for me was the rend spec, the damage seems much much higher and is doable without a great rift.
I didn't have any lucky pylons or great mob density and 60 was fairly easy, I was around Para 570 at the time. I'm not entirely sure how people are even reaching 70 with the BK build as it seems lacking in damage compared to the others, unless you're relying on a godly rift to fully exploit tornados.
Specific advice, your gems are really low level and you don't have a Hellfire neck, level your gems and make Hellfire necks until you get a good one.