Out of curiosity, what is it that you find yourself needing a bigger SSD package for? Tons of accounts? A few large files?
My use case is that I need only a moderate number of accounts (20) per VPS. But I need to allocate 5 GB of usable disk per account. Since part of each VPS disk is consumed by OS, swap, etc, etc, the SSD-5 plan only nets about 90 GB of available disk. Then leaving a little additional breathing room, say another 10 GB, that brings me down to 80 GB of usable space for client accounts. 80/20 accounts is 4 GB per account, which is short of the 5 GB I want per account.
Why not just reduce the number of accounts to 16, to get my 5 GB per? The answer is cost. I need to be at a level of 20 per VPS to make it work for me from a cost perspective.
Why not just do a dedicated? Again, the answer is cost. Not to mention that I really like the class of the processors in the SSD-X VPS's, and to get that kind of processor in a dedicated gets even more pricey.
So if there were a SSD-6 with 120 GB of disk, at a logically incremental price, I would most likely be able to do what I want.
A wandering and 'too-much-info' answer, but there it is...