While I don't have all the specs on the computer that my roomy is running Lennar Digital Sylenth 1, it's a Mac Intel Tower with 10 GB of RAM, so needless to say we're not hurting for power. I've used Sylenth 1 only in Logic Pro 9 and I'm not sure it's compatibility with other DAWs. I've never encountered any problems related to performance with Sylenth, as it always runs smoothly without issues. If you have a slower system I'd recommend printing whatever you do with it to save space, but that's always going to be the case...
Lennar Digital's Sylenth 1 is one of the coolest virtual synthesizer that I've used in a while. It brings a ton of great sounds to the table that are easy to manipulate in many different ways. I especially like Sylenth for it's great arpeggiator, which is one of the best of it's kind that I've used. I love the control here as you'll never run out of options and different sounds. The price tag on Sylenth isn't huge but it's incredibly cheap. Either way this shouldn't be the biggest factor if you're looking for a game changing virtual synthesizer like this one. Check out a demo today if you're intrigued as you should be!