And yes, some drives need more OP than others. Some (mainly newer drives) are coming with more built-in OP space unseen by the end-user. For example, an 840 Pro needs more OP than an 840 Evo, because Samsung has learned that write performance consistency can only be accomplished with more OP.
I think you have those mixed up. The Evos have more OP than the Pros.
But, the reasoning is solid, and the new Evos have pretty fair consistency, such that some people are choosing them
instead of the Pro, even with the budget for a Pro (but, if the Pro has OP user-added, it also gets faster, so you can have your cake and eat it too). We're also seeing the same pseudo-SLC cache tricks used with Toshiba/Sandisk MLC, at least with the new Sandisks, if not others (I'm not sure if anyone knows for sure if the new Toshibas do that or not, FI). With faster-writing MLC and added OP, you're better off, but the real-world difference is going to be very small, and likely not noticeable.
Users that perform lots of I/O, or mostly random I/O, may look closer (and generally choose a Neutron, M500, or Extreme II, depending on their location and budget), but for 99% of everybody out there, it's not worth much worrying over. The major flash companies have, each in their own way, made their drives good enough, and improved them in the right ways over time, for ever-better actual performance, and good enough longevity to last through being handed down through multiple PCs.
Except for super heavy users, this should be typical of the differences between them:
http://www.tomshardware.com/reviews/samsung-840-evo-review-1tb-ssd,3567-11.html
(sorry AT, but I guess Tom's has better SEO for some of their articles )
Useful AT page:
http://www.anandtech.com/show/7173/...w-120gb-250gb-500gb-750gb-1tb-models-tested/6
The Evo needs that added OP to compete, but it's right up there with the Pro, at a lower cost, and offers more consistent performance with the factory/minimum OP. But, as you can see, all of the newer SSDs from major makers are, in normal use, awfully close to one another in performance, as well, so aside from making a point to purchase one by a solid maker (Samsung, Sandisk, Toshiba, Plextor/Lite-On, Intel, Crucial/Micron, and Corsair's Neutron, as an odd-one-out), there's
much more worry than is justified; largely based on momentum, from the earlier 2008-2011 SSDs, many of which were craptastic in quite a few ways.
So just keeping an eye on the space may or may not achieve the desired result? It's best to make an unused partition?
Depends, If you have TRIM support, you
generally don't need to worry about it. Also, it's not a life or death issue. SSDs that
should have had more factory OP for desktop use will have better performance and use write cycles much slower, while SSD with sufficient factory OP will gain substantial performance, but not much in terms of reduced wear (and there's not an absolute best amount, either; how they implement wear-leveling is a factor, so one series w/ 7% might need more, while another with 7% might be fine w/o TRIM). Even with all that, most drives are going to last longer than the service life of their host PCs, by a significant margin.