My MBP boots in 15-18 seconds with my M4. And IMO it is a HUGE upgrade given you now will be protecting all of your files with a SSD. If you get a M4, I would get the 256 or 512 GB size (or at least the 128) because their write speeds are higher than the 128, and farrrrr more than the 64.
If you are going for the 64 GB size, the Samsung 830 has almost twice the write speeds of the M4 and the 95 MB/s of the Crucial v. the 160 MB/s for the Samsung is noticeable and so the 830 may be something you would want to consider. Once you get to the 120 GB size, then the difference really isn't quite as noticeable (the Crucial is like 175 MB/s and the Samsung is like 300 MB/s IIRC). Once you get to the 256GB+ size, virtually all SSDs will perform the same for MOST users, given they are all fast as hell and most users do not write enough data to see a difference. In real world usage, my Crucial M4 does as well or better than any of my other SSDs. I don't have a Samsung 830 yet, but I would not hesitate to put my most valued data on it for a second nor would I with any Intel drive (including the 520 after it has been out for a few more months).
But right now I favor Crucial because the M4 gets among the best (and often the best) of customer reviews (I am talking like 90-95% are 5/5 stars on every online site), and a few months ago when an issue arose, Crucial delivered on a firmware update in a timely manner...something which other makers have failed to do. Additionally, they have made it clear that they can and will provide support for us Mac users.
