“Rack” or “Wrack”?

According to Oxford Online, both are acceptable, wrack being a less frequent variation of the verb rack, in the meaning of 'cause extreme pain, anguish, or distress', and in a usage note they say:

'The relationship between the forms rack and wrack is complicated. ... Figurative senses of the verb ... can, however, be spelled either rack or wrack: thus racked with guilt or wracked with guilt; rack your brains or wrack your brains. In addition, the phrase rack and ruin can also be spelled wrack and ruin.'

Macmillan, Longman and Collins all accept wrack as an alternative spelling, although Chambers say it is usually regarded as an error.

Back in 1755, Samuel Johnson also listed 'wrack' with the meaning of to torture or torment, but says that it 'is commonly written rack'. - http://johnsonsdictionaryonline.com/?page_id=7070&i=2302

Michael Quinion at World Wide Words, also tends ton go along with this tolerant approach, suggesting that there seem to be good arguments on either side. - http://www.worldwidewords.org/qa/qa-wra1.htm

and he quotes Burchfield,from the 3rd ed of Fowler's:

'All the complexities of this exceedingly complicated word cannot be set down here: spare an hour (at least) to consult a large dictionary, esp the OED'

Daily Writing Tips has no such doubts, though - http://www.dailywritingtips.com/wracking-or-racking-your-brain/

Various tries at Ngram suggest that the wrack versions started around the beginning of the 20th century, and are far less common,with the 'wracked with' versions being a bit more relatively common than 'wrack your brains'.

The earliest 'wrack' version I can find at Google Books is from 1867, from the Dartmouth Magazine (US), although there's one with 'wreck' from the London Chronicle of 1759 - 'but whilst you wreck your brains, to construct machines to gain power ...'. But 'rack ' beats that by ten years, with this in The Monthly Review of 1749 - 'Now which of these was Celia's case, (Tho' all are common to her race) I shall not rack my brains about'. Most 19th century variations on (w)rack(ed) my/your/his brains at Google Books have the 'rack' spelling.

@WW
The article I read was in fact that by Michael Quinlon which appeared on World Wide Words..

Just an after thought:-
In the case of "----- and ruin" I am more attracted to the idea that "wrack" may be the more apt choice given its near similarity to "wreck" and indeed its original root.

@HS - Americans seem to go for 'Wrack and ruin', British online dictionaries for 'rack and ruin', with 'wrack' as a variant. This is the case at Oxford, Cambridge, Macmillan, Longman and Chambers. Only Collins lists it under 'wrack'.

Oxford give the origins as 'rack from Old English 'wræc' - 'vengeance'; related to wreak'. Etymology Online goes along with the idea that 'wrack' here in 'wrack and ruin' comes from Middle Dutch 'wrak' - 'wreck', perhaps influenced by OE 'wræc'.
http://www.etymonline.com/index.php?allowed_in_frame=0&search=wrack

If you use 'rack' for the verb, and 'wrack' for the noun, I don't think anyone can naysay that. But I think that there are arguments for the variants as well.

The Online Etymology Dictionary considers 'wrack your brains' 'erroneous', but
both Burchfield and Quinion were / have been contributors to the OED, and Quinion has made himself a bit of a reputation as an etymologist. If they say it's somewhat more complicated than that, I'm inclined to believe them.

http://www.oxforddictionaries.com/definition/english/rack#rack (see usage note)

OE wræc is also the root of wretch.

If you are racking your brains, then "rack" is best, as it refers to the instrument of torture.

It may be that people spell it both ways, but that doesn't change the fact that "wrack" is a mistake for the original "rack," i.e. "torture." Racking your brain doesn't mean messing it up or wrecking it.

Doesn't look good on proofreading site to find: "tends ton go along" (on this page)