On the subject of the toxins from antibiotics, hormones etc, unfortunately I think the answer is that we don't know, due to simple lack of evidence on the matter. By definition, the people who decide safe levels think the levels in food are safe, but their general outlooks seems to be that they don't know for sure, but there's no evidence of any danger. Fwiw, I eat tonnes of conventional meat and am sure it's beneficial compared to less conventional meat.
[Edit: This website- credit to Acton- suggests that contaminants in meat aren't a concern.]
The omega 6:3 thing is a worry. My solution is to not worry in general about the omega 6 in meat, but avoid what fat I can by trimming and pouring off excess. At first when I went high-fat paleo I thought "right, I ought to get start eating the fattiest cuts I can find!" but then soon realised that butter was likely far more nutritious (A, K2, butyrate) than animal fat and far less omega 6. I've heard the claim that properly raised animal fat should contain a wealth of nutrients, including goodly sums of vitamin D, but on paper (i.e. www.nutritondata.com it doesn't come across. Grass raised fat works out about the same as butter, just more MUFA less SFA (up to debate if that's good/bad/neutral). Stephan has a ncie group of charts comparing fats here.
For all that, I'd be tempted to use the tasty animal fat anyway, at least beef's the least omega-6y conventional animal meat!
This new piece has some nice graphs showing the differences between conventional and grassfed animals.