I strongly disagree. My Dell XPS came with a Hitachi 7k60 (7.2k 60GB) drive; I upgraded to a Seagate 160GB 5.4K drive with perpendicular recording, figuring that the dramatic increase in areal density would offset the lower rotational speed's impact on sustained transfer rates and seek times.
Hoooo boy was I wrong. The 5.4k is noticeably slower after downgrading from a 7.2k. Given the OP's situation-with a 4.2k drive-he'd notice a decent increase in performance either way. But honestly, I cannot recommend that anybody get anything other than a 7.2k drive at this point unless they have an older notebook and all they want to do is make it run.
I'm not sure I agree with that assessment either. Firewire 400 has a theoretical maximum transfer rate of 50MB/s. Firewire is much better at coming close to its theoretical maximum than USB 2.0 is, but you still can't expect anything more than 50MB/s out of it, and realistically it'll probably be closer to 45 tops. The 7k60 was one of the first 7.2k laptop drives and even it was hitting about 45MB/s sustained in HDTach and ATTO. The newer drives with larger buffers, SATA, perpendicular recording and more than 3x the areal density aren't going to be slower. I wouldn't at all be surprised to see a modern 7k laptop drive benchmark faster than a desktop drive handicapped by a firewire 400 interface.
There's also the portability issue of a firewire drive... It's basically a non-starter.
The OP stated he wants speed. If he wants speed, the 7.2k is the only realistic choice.
I don't think anyone here will deny that the faster rpm drive is going to typically benchmark faster than the slower drive. That is a no brainer. If mshale was only looking for the best speed, there was no real reason to post the question to begin with - he could have just gotten the 7K drive.
Rather than just creating posts to state your disagreement with others, how about some actual input for the OP. And rather than showing off your knowledge, how about some real world advice and your opinion for the OP's questions.
The questions were:
1) Can someone hand me down some advice?
2) Would it be worth spending $200?
And the only real info we've been provided is that he stores movies on his drive.
As to my point - I have done many timed tests between USB, FW400 and FW800 on my MBP and have posted some of them on these forums.
What I'm talking about is in response to the above questions and comparing spending $200 for a new internal drive, with the result of now having a 200GB drive that requires a further expenditure for an enclosure for it - or spending about $175 on a good external 500GB drive with FW400. He now has a total of 700GB storage space and my best guess is that the new, empty 500GB drive will be, real world speed, about as fast as his current 4200 rpm internal drive that is probably starting to get filled if he has very many movies stored already.
And bottom line - as I pointed out in my previous post - the difference in cost is really relative to each individual and what they are looking to achieve. In time, we all learn that exploring multiple options is the only way to know that the current choice we're about to make is the correct one for us. The answer for one user is not necessarily the same as for another.