I didn't realize that the 900 was a 900 MHz chip... is it a Celeron? My 900A has the Atom n270, an impressive little processor, IMO.
SSD's can be found which have been rated for their read/write speeds. I upgraded my EeePC 900A (the Best Buy custom version from 2009) from the stock 4gig, to a 32 gig.
I did not purchase the SSD which had the highest speeds, the one I got was rated only about 2x as fast as the original SSD.
I selected my SSD according to capacity first, price second, speed third. I purchased from a company that designed a range of SSDs to fit my EeePC 900A (the 900A uses a weird form factor along with an uncommon data interface).
Still happy with my selection. I got mine from Active Media Products, my exact part number has been discontinued because a slightly faster version took its place for about $20 more (over time, that price should have dropped. but that's a different story).
One observation I'd put out there is that there will still be pauses between drive accesses, to let the CPU make decisions, to write comfiguration files and logs, as well as other hardware slow-downs. That said, on the new drive, I was able to boot a full install of Bodacious Bacon (lol! "Bodacious Bacon" refers to k u b u n t u) (NOT a version optimized for netbooks) in about 35 seconds. My cellphone needs way over twice that time!!
My point here is that the fastest possible device might not be the only option to offer improvements; I got more capacity and faster speed for a low price - that combination was hard to beat at that time.