Which would YOU choose, and why?

Like lots of people, I'd really like to increase my data transfer rate from
the hard drive.  Right now I have a 15ms 210Mb IDE drive (Seagate 1239A), and
a standard IDE controller card on my ISA 486-50.

I'm currently thinking about adding another HD, in the 300Mb to 500Mb range.
And I'm thinking hard about buying a SCSI drive (SCSI for the future benefit).
I believe I'm getting something like 890Kb/sec transfer right now (according
to NU).

How would this number compare if I bought the state-of-the-art SCSI card for
my ISA PC, and the state-of-the-art SCSI hard drive (the best system I could
hope for)?

Obviously money factors into this choice as well as any other, but what would
YOU want to use on your ISA system? And how much would it cost?

Along those lines, what kind of transfer rate could I see with my IDE HD's if I
were to buy the top-of-the-line IDE caching controller for my 200Mb, 15ms HD?
And how much would it cost?

Thanks for any comments.