Losing performance?

If i was to get a Raptor 150GB at what point in GB would i start seeing slower load speeds becuase im getting near to filling the drive at.

eg 90GB, 110GB, 125GB etc.

And would one Raptor 150GB and one Seagate 250GB work in a RAID-0 and RAID-1 setup?

thanks

For RAID to work you need two identical drives.

Ok thanks what about my other question?

Disk performance reduces lineraly with more use.. yes when your approching 110Gb used the last data placed on the drive will take a small performance hit.. but you use a decent defragger to make sure that information isn't critical to performance.
Or you can partiton the drive when you install your OS/apps so that a storage partition in the slowest portion of the drive.

I see how much would you recomened on setting a O/S partitions, i will be using VISTA?

Also one more thing when i separate the drive into 2 partitions, i install windows on the first partition through the format process and then when i have gotten into windows my second part of the partition will be completely empty right and then ill just have to format it? is that right.

Similarly if i have two hard disks i install the O/S on one then the other one ill just format it when im in windows right?

Looks like Vista alone will be about 15GB, so add in the rest of your programs from there to get the estimation of what size you'll need. Yes and yes to the rest of your questions.