Option 2 for me...
 

It may involve Jetlag, BUT you'll get:

Guaranteed 1.0x membership miles to BMI
Guaranteed 2.0x destinations miles to use next year
Cheapest of the options if you time it right (£200-£250 all in)
Can be done on an overnight (Sat-Sun) if necessary according to fare rules - or more if you fancy a couple nights in BOS/ORD/NYC. (Good time to go skiing for a couple of days north of Boston)
Guaranteed better seat for the money with your * status.

Although jetlag sucks, I'd suggest that the 2 long-ish bizz tickets that you'd need across Europe will probably involve more time "wasted" in airports/planes than a Trans-Atlantic to the East Coast ever could...!

Option 2.

Moreover, with the Saturday lunchtime flight out, and the Sunday daytime flight back, where's the jetlag? Dep 13:20 GMT. Arrive 21:10 GMT. Dinner, drink, bed by midnight (GMT). Back via IAD on the Sunday. Depart 07:25 local (12:25 GMT). Back in LHR 21:55 GMT. In bed by midnight. Stay on British time throughout, everything's in your normal waking hours, and as you won't need to sleep on the flights E+ is acceptable with a good book (or four)...

Plus, you'll be able to do the whole thing (airport hotel included) for well under £300. It's a no brainer.

This load of horse feathers is simply out of date. I can assure you that BD economy fare get 100% on transtlantic flight. And I'm 100% sure of this. (LH, SK etc. will screw you for lower multiples, though).

I recommend Option 2 also - for all the reasons Wingnut points out - and the bonus miles on UA at the moment.

So, JCEP, has the poll closed?

Yep, the poll has closed! A landslide; it's the UA mileage run. As Wingnut stated, it's a "no brainer", although sometimes we need the wisdom of others to show us how obvious a decision it really is! Thank you. Will probably do the non-stop IAD run, out Sat and back Sun.
An issue though; Ms. JCEP thinks I am nuts and may physically restrain me if I try (might be worth it then!).

Not sure if it is another boob... but according to the bmi website (which they claim is now up to date), Z class UA (business) fares only accrue x1.0 miles!

Maybe worth checking out if Biz is a good option for you.

That, I know from personal experience, is correct. It is also the case for C fares on Air Canada - a £2.2k Biz ticket to Montreal will only get you 6,482 miles if posted to DC!

Oh no, it gets better than that!

bmi will sell you a fully flexible Business ticket to YYZ for £4,000. That's a C-class fare, the highest BD sell. But, whoops, the operating carrier's mileage rules apply -- just 1x miles on AC then. What about the person to whom BD sells a restricted D-class ticket? AC doesn't use D at all -- presumably zero miles for that £2k ticket.

If you fly a BD codeshare on SAA metal, I presume that you do not receive status miles? SA isn't a * carrier yet, and, 'the operating carrier's rules apply'... I could go on.

I sent DC an email querying all this silliness -- I have, of course, received no response yet.

A better class of thievery!

Actually, J class is used for full-fare business on AC.

You're absolutely right -- I should check myself before I type. I meant D class. In fact, a J ticket (cheaper than C on BD codeshares) would be worth 2x. All so ridiculous :)