How do you compare the value of LY points vs. miles on other airlines, say AA or BA, for example?

I ask because I'd like to take advantage of the LY special until the end of March where a bonus economy ticket costs just 650 points (usually 900) to Europe. To London, for example, the ticket would cost 650 points plus $222 in taxes/surcharges. If I use another 200 points to knock off $100 from the taxes/surcharges, then its 850 points + $122 to London.

OTOH, to London on BA using a AA miles, its 40,000 miles + $126. Dollar to dollar its a wash. But how do you compare the 850 points to the 40,000 miles?

Here's what I thought, tell me if this makes sense: We know that it takes 1400 points (usually) to get a Bonus Y tkt TLV-NYC. To get those 1400 points, it takes 3.5 roundtrips, with each one yielding 400 base points (forget the PL/GL bonus). On AA, by comparison, it takes 90,000 miles to go TLV-NYC. And to get there, you need to fly 8 RT's (11,300 roughly per RT). 11,300 (miles from the trip) divided by 400 (points from the trip) yields a factor of 28. 40,000 miles then would be equal to 1428 points - I think. So that AA charges for TLV-LHR as much as LY charges for TLV-NYC in miles/points. It would seem that El Al's awards are much cheaper than AA's and hence LY points are more valuable than AA miles. Does this work out? Am I missing something?

Of course this whole theory is upside down when you consider Amex points' transfer rates. With all the "miles" programs, 1 Amex point is equal to 1 airline miles. But with El Al it works differently so that it takes 97,000 Amex points to get 1400 el al points. Meanwhile, 90,000 AA miles (which are similar to Amex points), according to my assessment above, is equal to 3214 LY points.

I am a bit confused.