The ideal Tormek model?
For me, the ideal Tormek would be the like new old square frame Supergrind at an estate sale for fifty dollars. 
Since my ideal probably doesn't exist, the choice is probably between a T 7 and a T8. (Used prices are often too expensive to be good values.)
One of the commendable principles of Tormek is compatability of the latest advances and jigs with older Tormeks. In my opinion, thr most outstanding feature of the new T8 is the new SE-77 square edge jig. This jig will work with any Tormek. The new zinc housing and water trough are certainly very nice, however, I do not see them as must upgrade immediatly features.
I admit to being a Tormek junkie. I am also a thrifty person. I would probably opt for the T8 and tighten the budget in other areas. That's just me. If there were no T8, I would be quite content with my stalwart T7, and even more content with the new SE-77 jig.
For someone working with knives, I don't know how much the improvements of the T8 would translate into benefits. The hundred dollar saving could be a considerable factor, depending on one's budget. There is no wrong choice, only individual choices which may be morebeneficial.
Ken
Ken, going to differ with you a bit, from experience.
Sub $200 on an older Tormek, with a bunch of jigs and a decent stone, is/was a good buy for me. I did upgrade to the quick release, stainless shaft. A bargain would really depend on what it came with (stuff you will use, or not).
For someone working just with knives, like a chef, and the factors of the SJ stone is also available on the T4 as well as smaller and lighter (probably stored on a shelf or under a table), IMHO, I think that might be a better buy for them. (as compared to someone like SteveBot who does all kinds of sharpening at markets and such) Again, situations vary, so would my advice.
The S2000, years back, used to have a rust issue at the base. I looked at the T7 bodies (and from memory they were powdercoated), when I looked at several used Tormeks online. The cost of a new body, drove the used Tormek price, way over retail. (most of those I looked at, were the old square frame models) The new zinc base, should eliminate that, completely. (I got lucky on mine, what I expected to be rust, was would particles and glue, from a benchtop, why I didn't have to refinish mine)
The water tray, and new lift mechanism, is an improvement for some of the older woodworkers I have known. One gave up power tools at 95, after cutting off his fingers on the table saw, but still appreciated hand tools, and wasn't in a hurry. (since passed on)
I would think in typical fashion, the frame may be upgradeable on our older models (where it has been before, but the jigs haven't always been), but wouldn't be cost effective.
