Adverb for "Cannot be topped"

What's a good adverb to indicate an attribute that cannot be improved upon?

I wanted 'untoppably' to be a word, but it isn't.

Optimally and its synonyms come to mind, but it doesn't really have the best fit for the phrase I have in mind:

I’ve thought up a pretty neat method for completely eliminating dynamic cell references. I wrote it down for later. You can look forward to an [untoppably] fast version whenever I get a free week to implement it. (Could be a month, could be a year)

Optimally is probably the most accurate word in general, but a good fit for the phrase you give is unbeatably:

You can look forward to an unbeatably fast version.

I think insurmountably would also be a decent answer.

Some more possibilities:

incomparably
supremely
exceedingly
transcendently
inimitably
unsurpassably
uniquely
unapproachably
peerlessly
unmatchably
invincibly
unsurpassedly

The adverb I would use is insuperably. From the adjective insuperable. (not "toppable")