The INuke DSP1000 suggested by Carson79 looks very interesting - I note it has delay options - some tactile enthusiasts set a delay within their system. This is beyond my level of experience and understanding, but I am sure Carson and Logiforce know about this.
The BK Gamer transducers probably won't be powerful enough for you - I know Mr Latte has recommended using the BK mini LFE units instead.
Greekbull has used BK Gamer and Aura Pro bass shakers and commented that he got a better effect with the Aura Pros.
I've experimented with the Aura Pro bass shakers and found them to be excellent. I've also got four Sinus Live Bass Pump 3's (a European cut price alternative to the Aura Pro, but not quite as good) and a BK Advance.
Tactile is a field which can be addictive (witness Carson and Mr Lattes setups!) also we don't yet know what GT6 will be like from a tactile standpoint so I would err on the side of caution at the moment. Some GT5 cars provide excellent tactile feedback (notably the Mercedes Benz V8's and the Audi R8 V8), however many of the cars in GT5 provide almost no effect - so all you get are kerb bumps. GT6 might be better, exactly the same or worse.
My suggested approach would therefore be to make sure what you get is easily upgradeable and be cautious with the spending until we know more about GT6. Also, build or equip your rig with multi-channel tactile in mind even though you might select just a mono setup for now (shaker under the seat and pedals adds a lot to the immersion) or stereo (2 shakers under the seat and 2 under the pedals. Isolation is key to good tactile and especially multi-channel tactile - isolate the rig from the floor, the seat from the rig, the pedals from the rig and the gear shifter from the rig. The better the isolation, the less power you need which can allow you to use smaller amps and cheaper tactile transducers. Also the medium is very important - that is why I suggested a kirkey type seat. I have a metal framed chair with which I did a lot of testing and one Aura Pro 50W shaker was enough for a great effect. I use a wood framed seat for console racing (wife won't let me have a full rig!) and even with 4 shakers I get less effect - hence upgrading and adding a 300W BK Advance.
Some of the things you implement on your console rig will be applicable to your PC Simvibe rig - my understanding is that simvibe works off data not audio with the result that you need to add audio to get a full tactile effect (stereo audio tactile would add curb thump and collisions).
I've just edited to add - what games are you going to play on the consoles? There will be people who use this site who will have tested the tactile effect on each game on PS3 and Xbox. I've only tested GT5 - variable car effects, good offroad and kerb effects. Dirt 3 was very poor - no tactile effects noticeable.