515 - 525 side by side comparison

Hardware and performance gurus:

At the lower end of the scale, can you see an advantage to getting a 525 over a 515? Lets say you have 30 users, need 200GB of disk space (you are at 75% utilized at 52GB now but plan for some growth) and you plan to get 4GB of RAM. Most of your processing is interactive RPG programs that update data with minimal amounts of batch processing. You are doing some web based program hosting but not much, although you expect that in a couple of years you may be replacing more of the RPG 5250 programs with RPG CGI-type web programs. There might be some Java web applications running. You don't need LPARs and the user population might grow to 45 or so in the next 3 years.

I don't see any compelling reason to buy the 525 over the 515. Or am I missing something? Unless you are in a high growth situation, it seems to me that the 515 wouldn't run out of gas before it was due for replacement in 3-5 years. Since there isn't a limitation any more on the number of users a 515 can be licensed for, even if you doubled the number of users, I can't see where a 525 would be the better choice. The only thing I can think of is that more disk arms will improve performance, but if the data store need is modest, putting in a bunch of disks to improve performance seems like overkill.

Seems to me there is a bit of overlap at the low end of the 515/525 scale. What say you?

Thanks,

Pete Helgren