i don't have experience using one on a 911, but i have a cheap 10ton one that does nearly everything i need, although its struggled a bit with some really old and knackered wheel bearings before. I put them under pressure, then worked them with some penetrating spray, some heat, freeze spray, etc. until they went. if you're dealing with some proper old stuff that's really stuck you might look at a bigger one, but I would have thought 10 would be big enough for most if not all of what you'd encounter - my local porsche specialist has a well-worn 10t press that does everything he needs and all the stuff i can't cope with myself on mine!
there's a sweet-spot price-wise somewhere around 10ton i think (can't remember exactly) above which prices shoot up.. If I was spending more than I did on my little one then I would have still got a 10t one but with a pressure gauge and taller (ie more space to get things in) as I think thats more useful than more force
One thing to think about for suspension bushes - take a look at the arms and things you're going to be removing bushes from (in particular which direction they need removing in) and that might dictate which size (physical) you need.. i know for two of the four trailing arm bushes on the e30 i did in the spring i had to use a much taller press with more space to get in there properly. It didn't need the full capacity (pressure) but did need the space!
Also you might want to get some press tool things (don't know the proper name) for removing bearings etc - they're basically just stepped discs of steel but it means you can get properly onto whatever you're trying to press out and press it straight without deforming it. Using impact sockets might work, but it aint right!
Also make sure you have some decent blocks and things to put underneath and support the parts..