Do you need a polysynth of monosynth? It seems like you're looking at both.... do you need something with a built in sequencer? Do you need a keyboard? You listed 2 true analog synths and 2 modelling synths in there too.... have you heard them next to eachother? The virus is anlog-like but really has a sound of its own not unlike the nord lead.... its very modern.
original Detroit techno actually relied pretty heavily on FM synths... Derrick May is a noted DX100 user... a lot of Juan Atkins' classic stuff is loaded with FM sounds as well as the Korg MS10 and Sequential Pro One (so looking at Dave Smith synths isn't far off, but the OB6 is an oberheim reissue with the 2 pole fitlers and much slower envelopes than the harsh/snappy Pro One, way different sound, so you are looking at the wrong Dave Smith synth for traditional techno, oberheims are more of a synthpop thing, look at the prophet range unless you are looking to do something all your own)... and the MS20 reissue will cover all of the noisey sounds pretty well though I have never been a fan of that synth, just its filters and noise gen and even then the mono/poly filter is wicked too.
For 4 operator FM sounds the world's your oyster as there's the new Korg Volca FM module as well as Yamaha's new mini keyboard DX synth... and the old Yamaha TX racks that were also popular in 80s/90s Detroit are still readily available on ebay for a pittance. Techno also relied heavily on entry level lofi samplers from ensoniq and roland, though Akai eventually took over as the Detroit sound became famous and these guys had more money to play with. Octave One created the popular glitch vocal samples because they ahd trouble programming their Ensoniq sampling keyboard (I want to say it was an ASR10 but I think it was actually an even older, grittier sounding model). Old digital samplers have a sound though they are a total PITA to program as are older FM synths.
I am not a huge fan of the Virus as it is a jack of all trades. master of none... but if you can only buy one synthesizer the Virus will cover a lot of bases and is geared towards techno and acid house sort of analog noodling right out of the box without reading the manual. I wuld like to own one just as a utility module, but I never seem to bite the bullet on the buy in because there's other cool stuff out there that's cheaper and more interesting.
I have a sub phatty and a midi moog SE1, they both sound great. I seldom use them for techno though.
I get a lot of mileage out of my x0xb0x, Bassbot and Volca bass for techno and use them for much more than just acid twittering.
Also, the Juno 106 was huge in techno circles (as well as every other genre of electronic dance music) and still is. Its been ehard on more dance tracks than probably any other synth. I think roland system 8 can simulate it as well as a million other synths from their golden era, but god knows how accurately.
in old, underrated synths ensoniqs ESQ1 and SQ8 are killer wavetable type synths with tons of highly tweakable digital envelope and LFO generators as well as analog Curtis filters like you used to get in later Oberheims from the Matrix series that have a more aggressive, techno sound. They do require some menu diving, but they can handle ANY job. The Korg Poly800 is a good old DCO analog beast that's in the alpha juno camp but warmer.
and then there's the ARP Odyssey. Damn it sounds great. Its a real workhorse analog monosynth reissued by Korg very accurately in a mini key version or a module. I love mine and use it constantly, even just to make horrible noise after work... it has less deep bass and 1 less oscillator than your average moog but the synth is also less sloshy sounding and has better cut than a moog for leads.
If you want a moog monosynth that can also cover early oberheim sounds look at the Studio Electronics SE1 or SE1x, itstheir MIDI moog under a different name to avoid trademark issues but they also added some new features including oberheim 2 pole filtering.
everyone likes the bass station 2, I had a super bass station rack way back when. It was okay. The new one sounds pretty similar. Its like a more aggressive SH101 to my ear. The Arturia Mini and Micro sound really cool and can produce some very ahrd analog sounds for techno. I find them to be more in the Dave Smith camp than roland. Very biting and 'out front' in a prophet way but more versatile and very stable.
ugh, I could go on and on w/o giving a ton of info.... I suggest buying new from a retailer with a no-questions return policy
you should go and read all my synth reviews as I've been pretty detailed.
These guys also really know their shit:
http://equipboard.com/v8project
http://equipboard.com/whorse