I find the current SLI boost to be a lot better than 'underwhelming' considering it is currently running in probably the most inefficient way possible. Proper SLI support can only result in a vast improvement still that current SLI users will get for free.
Fair enough, since I did say "currently", which is not accurate. I gave up on SLI about 3-4 years ago.
But I highly doubt it's running in "the most inefficient way possible". Granted I haven't SLI'ed in about 4 years, but when I did, the "whopping boost" was about 25%-30% in most games. So, if it's running worse than that then you're correct, it's running in the most inefficient way possible, but I rest my case about underwhelming. If it's running better than that, then it's not the most inefficient way possible and NVidia has improved on the concept. Maybe I should revisit it.
And as a preemptive strike, I've been gaming since 1995. All but my first two video cards have had custom OC/OV bioses and I've done hard volt-mods to several others. However, marriage, a son and real life have derailed my gaming enthusiasm.
YMMV