SEO with throw-away slugs

[villas]

Dear all,

I plan to do this:

1. Use the url format  e.g.   myfunction/1234/meaningless-slug-version-1
2. Google will index the url
3. I later change the slug to:  myfunction/1234/meaningless-slug-version-2
Problem:  Google might now flag "duplicate content" and/or confusion

To resolve the problem (in pseudo-code):

def myfunction():
    row = db.tbl(request.args(0))
    if row.slug <> request.args(1):
        raise HTTP(301,'Redirected <a href="%s">here</a>' %newlocation,
                   Location='myfunction/1234/meaningless-slug-version-2')

My idea is now Google will see:
a) that my old url is permanently redirected, 
b) there is no confusion in Google's index, 
c) I do not need a canonical tag

Disadvantage, my site is a bit slower in respect of the old urls.

I am not a SEO expert,  so I would appreciate any comments and criticizism of the above and any other tips/strategies that might spring to mind.

Best regards,  D