Yes there will be differences in performance. The ones with the bigger chaches will be slightly faster.
For the rest of it... go with Western Digital or Maxtor...Forget IBM and buy Seagate at your own risk. There will be slight performance differences between them, but it's damned unlikely you will notice it without using benchmarking software. Most people won't notice performance differences less than 50%... really.
Don't get all caught up in benchmarks and piddly 1% differences... look at the warranties, quality and cost of the drives.
Maxtors were noisier, due to their fast seek times (D740X series). But apparently the new diamond max 9 line is alot better.
I prefer drives with 8Mb cache as it improves the handling of lots of small files. improves performance noticably.
As for 8Mb cache drive differences between manufacturers i dont think theirs much difference. not enough to be noticalbe to the casual user. So i go for drives that are quieter or have longer warantee's (the W.D. JB line still has 3 year warantees')
I had a couple of DOA Seagates a while back and had one hell of a time getting them replaced. The distributor I bought them from finally provided Maxtors as replacements and told me he was pissed at Seagate.
As for the quiet thing... Almost any harddrive can be quieted down significantly by putting them in a fabric padded drive bay.
The process is fairly simple...
You will need some soft fabric (the heavy cotton they make T-shirts from works well) and some double sided carpet tape (the thin kind, not the one with the foam in it).
Simply peel one side of the tape and press it down onto the fabric so that you have a strip of fabric covered tape.
A little measurement, cut two pieces the length of the drive bay and a little taller than the drive.
Next slip the drive in place and pencil line the sides of the bay so you know where to stick the tape.
Take the drive out, peel the other side of the tape and fit it into the drive bay, being very sure you don't get any wrinkles.
Now use an xacto knife to open the screw holes.
Finally slip in the drive and attach it in place with plastic screws.
It should be very quiet as this padded mount method prevents all mechanical vibrations from transferring into the case, which acts like a sounding board.
The whole idea is to stop any vibration from the drive from being transferred to the case.
I did this on my own machine... My drive is almost silent when just spinning, I still hear a bit of seek noise but it's sort of a dull "bump" sound now instead of a very annoying "snap". The fans drown it out very nicely.
The fabric method provides a soft contact area all along the side of the drive and only reduces the bay dimension by the thickness of the cloth. Most bays are a wee bit on the wide side anyway so this shouldn't be a problem.
If you can't get the plastic screws (The ones I use are actually for mounting transistors, get them at an electronics supply house) you can always put a little scrap of fabric on the outside of the bay where the screws go in and use a normal metal bolt with a washer to isolate it from the case.
With the rubber grommet method you would probably have to modify the drive bays to get the grommets in place without having to use a sledgehammer to get the drives in... Dimpling the sides of the bay to accomodate the grommets probably puts you at risk of metal to metal contact should things not be exactly square.